bytemaster0

Hello all,

First off, I am generally very happy with my 2014 GLK250 BlueTEC. It now has a bit over 10,600 miles in just a bit over 5 months. The ride is fantastic, the handling is very car-like, and the technology and quality are second to none. In short, it is a Mercedes-Benz. However, one thing has been starting to drive me crazy, and I'm very curious if others have experienced this as well.

When I first purchased the car, I noticed on some occasions that at speeds between 45-60MPH on some road surfaces, I'd hear a low, resonating sound (probably 30-40Hz) that would pulse in and out at 1-3 second intervals. I quickly blamed the road surface, or perhaps that my tires had settled a little bit while sitting on a surface. Often, the noise isn't there, and when driving at 70, it's basically non-existent.

Now that Spring has arrived, and that I have removed my winter tires (yes, the noise also happened with them), I am especially starting to notice this cavitating or resonating sound being caused by many different sources. If I go over even minor bumps, the resulting sound is a boom that I can feel. The pulsing version of this sound at 50-60MPH is inconsistent (it happens mostly if the wheels are unbalanced or if the tires are a bit stiff from sitting in one spot), but I can deal with that. In short, it feels like I have a subwoofer in the back of the car!

It has become clear to me that a possibility is that this sound frequency happens to be the natural resonant frequency of the air cavity in the car, dictated by its length (or at least a harmonic). If this is in fact a resonant frequency, then all GLKs should do this, not just mine, as they are all the same length and size. Again, it's a 30-40Hz rumble (when repeatedly excited by the road) or boom (when triggered by an impulse, such as a bump). As I have sensitive hearing I am noticing it more and more, now that I can't "unhear" the sound. I even ran a frequency analyzer on my phone to confirm that I wasn't crazy, and it definitely seems to show a higher peak in the very low frequency sound range.

Has anyone else heard this in their X204 MOPF (2013+)? Are there ways to mitigate this? I've searched online, but Google seems to be quite stumped by this question, and returns no useful results. If anyone has this experience with their GLKs, please post. Thanks!

bop11

If you open a back window slightly does it go away? If you turn off your heater/AC completely doe it get better or worse? Do you have a sun roof?
Also check the rubber at the top of the windshield for looseness.
Is it more noticeable if you are in the center lane of a highway next to a divider wall (Jersey barrier)?

420tee

I get a similar noise at nearly any road speed if I run one rear window down with the front windows closed. It can feel like it's going to blow my ear drums out. Mine's a 2011 GLK. Very annoying.

RSNovi

A slightly different annoying sound. When I test drove a 250 at the dealership at very low speed there was a loud resonance from the engine. I even read about it in reviews too.

Having my car for a week so far I haven't noticed it on mine.

Chris

bugelrex

I get this too on a 2013, I haven't bothered to bring it up to a dealer yet.
Some wind is catching on the door seals I think

beejonnybee

My 2011 is humming as well, especially on uneven roads. I thought about, but haven't try yet, is to shut close the trunk cover (mine is always unshut). Try that?

bytemaster0

Opening the windows all the way and even the roof seems to have no effect, which is odd. Vents have no effect. It's just the bumps themselves, and any vibrations that may be induced by the road. One would think that if the car is forming an air resonance cavity, that opening windows would surely affect it.

However, I did one test that I think will put the *AIR* cavity theory to rest: I drove with the liftgate open, over the types of bumps (very small but noticeable ones) that seem to induce the booms from the rear. No change.

The bumps that are the boomiest tend to be depressions in the road, formed by expansion and contraction of the road surface during seasonal changes. They are sections of the road that are "V"-shaped, meaning they dip in. The rear wheels bump up suddenly over these, once the wheel comes back up the slope of the depression, and these make the loudest booms.

So, does this mean that the cavitation/resonance is happening along the car body, and is independent of a natural resonance cavity in the air, which may be at a different frequency? Or is it that the car is just so quiet and noise-isolated that natural impulses just sound louder? Still, when going over rippled concrete bridges, the sound can be overwhelmingly-loud. The suspension is pretty stiff in that car, which is one of the many reasons it has such great handling. Perhaps this stiff suspension causes quick bumps to be transmitted to the car body more effectively.

One last possible tidbit: the "boominess" and overall resonance *MAY* be temperature-related. I especially noticed the sounds when the temperatures were in the 60s (F), and now that it has cooled to 50, the characteristics seem less pronounced. This may all be in my head, but if it's true, it may lend credence to the body-based resonance, which changes as the temperatures change. I will need to find some recording equipment to see if that theory holds, and do a frequency analysis of my drive home.

I tried this. It doesn't really help.

Either way, I'm just hoping that I will become less sensitive to this. The more I drive it (and boy does this car drive well!), the less it's an issue.


Thanks for all the posts/replies, if anyone has additional thoughts, I would love to hear them. Thanks!

ble2716

Apparently, my co-worker's B200 has exact same issue.

420tee

I give up, whats a "trunk cover"?

beejonnybee

or tonneau cover, the slide out cover that cover your trunk / storage area.

grane

a PANO roof?

These have been an Achilles heel, not just for MB. A whole litany of complaints and issues....

The PANO maybe causing the problem. That's why we ordered our specifically without it.

Have the dealer check it out....INSIST it be made right.

panoff

Did you ever find the cause of this? - I just bought a 2012 GLK and am experiencing exactly what you're describing. I have an appt at the dealer next week and was wondering if you had something I could suggest for them to check.



Opening the windows all the way and even the roof seems to have no effect, which is odd. Vents have no effect. It's just the bumps themselves, and any vibrations that may be induced by the road. One would think that if the car is forming an air resonance cavity, that opening windows would surely affect it.

However, I did one test that I think will put the *AIR* cavity theory to rest: I drove with the liftgate open, over the types of bumps (very small but noticeable ones) that seem to induce the booms from the rear. No change.

The bumps that are the boomiest tend to be depressions in the road, formed by expansion and contraction of the road surface during seasonal changes. They are sections of the road that are "V"-shaped, meaning they dip in. The rear wheels bump up suddenly over these, once the wheel comes back up the slope of the depression, and these make the loudest booms.

So, does this mean that the cavitation/resonance is happening along the car body, and is independent of a natural resonance cavity in the air, which may be at a different frequency? Or is it that the car is just so quiet and noise-isolated that natural impulses just sound louder? Still, when going over rippled concrete bridges, the sound can be overwhelmingly-loud. The suspension is pretty stiff in that car, which is one of the many reasons it has such great handling. Perhaps this stiff suspension causes quick bumps to be transmitted to the car body more effectively.

One last possible tidbit: the "boominess" and overall resonance *MAY* be temperature-related. I especially noticed the sounds when the temperatures were in the 60s (F), and now that it has cooled to 50, the characteristics seem less pronounced. This may all be in my head, but if it's true, it may lend credence to the body-based resonance, which changes as the temperatures change. I will need to find some recording equipment to see if that theory holds, and do a frequency analysis of my drive home.


I tried this. It doesn't really help.

Either way, I'm just hoping that I will become less sensitive to this. The more I drive it (and boy does this car drive well!), the less it's an issue.


Thanks for all the posts/replies, if anyone has additional thoughts, I would love to hear them. Thanks![/QUOTE]

grane

We were loaned a 2015 GLK with a PANO roof whilst our 2013 )no PANO) was in for service. We had the former for a week or so.

The 2015 does not have the "boom" problem described. The 2013 does.

Yes, it seems to occur most where there is an oscillation such as caused by frost heaves. It is worst in the rear. It sounds like the shocks/springs are hitting their bump stops. We are using stock 19" wheels and 17" winter wheels/tires per the recommendations in the OM. BTW this is not a seasonal problem. It happens on any road type described at any temperature with a single driver or a full load. It doesn't matter if the windows are up or down. Our two other MBs don't have this problem.

We have complained to the dealer several times but have gotten no satisfaction. Seems like this is a problem with vehicles from 2013 (perhaps 2012) on but 2015 seems to have left it behind...

I shall trace the part numbers of the 2013 versus the 2015 to see if there is a difference and report back.

panoff

Thanks for the reply. My 2012 has no PANO roof. I saw this posted on a MB website elsewhere:
BOOM: A hollow, low-frequency sound/sensation, this makes you feel as if you're riding inside a metal drum and the atmospheric pressure is rapidly changing between positive and negative.
On rear wheel-drive cars, check out the driveshaft and its u-joints because if it's spinning out-of-true, it will cause waves that push up on the floor of your car.


Curious if your service tech ever checked that out?

Juliet Sierra

An old thread, but to me a new problem.
Bought a used 2014 GLK250. Road noise is quite loud. No sun roof to blame.
Interestingly, the vehicle is quieter when towing a trailer... So it seems (and feels) to me that the suspension is a little stiff for non-towing use and that is exciting the body to resonate.
Anyone see an improvement after changing shocks? How about using sound-deadening material like "Hushmat"?
Thanks,
Jim

panoff

After several trips to the dealer, and with different technicians at hand, it finally turned out that the motor (and transmission) mounts needed to be replaced. After that, the noise, while still there, was much lower. The remaining noise was roughly similar to the sound I hear when driving in another GLK 350. I later replaced the rear shocks and the noise diminished even further, but the biggest change with new shocks was that the ride improved immeasurably.
Good luck getting them to really look at the motor mounts. Fortunately, mine were still under the extended warranty.

CarbonKevinYWG

Suspension systems (passive, that is) don't cause any excitation. Ever. They react and interact with excitation that comes from other sources.

For your particular set of variables - dampers, load, springs, tires, speeds, and road, it sounds like you're experiencing an "overdamped" response, and when you add the mass of a trailer, it shifts the response towards "critically damped", which is ideal.

The vehicle needs to feel stiff when unloaded so that it can still operate safely when it is loaded with a lot of cargo or a trailer. It's simple safety design. Unfortunately we have to accept that tradeoff, and I happily accept it because it's the safest solution for everyone.

No, adding hush mat to your vehicle's sprung mass won't do anything for suspension performance. That's just adding a (very!) tiny amount of sprung mass to the system. It might kill some panel resonance, but won't do squat for your ride quality.

Yes, changing dampers will impact ride quality significantly, but a less aggressive damper should be paired with a softer spring. Keep in mind you're impacting your towing capability by doing this - you risk moving into "underdamped" territory, which can be dangerous.

Juliet Sierra

Kevin, thats what I suspected.
I went the other way decades ago with a late-80s Jeep Cherokee. It trailered poorly until changing to firmer shocks, Monroe Gas Magnums. Then it rode almost as firm as the GLK250, but the maximum safe trailer speed was vastly improved. The trailers towed are about 30' long with one axle, you can imagine the concern about stability.
Do not want to get too soft for trailering but at the same time would like to get rid of the ow frequency noise. Air adjustable shocks may accommodate with and without trailer, but shock change is pretty much a last resort.
Waiting to hear if anyone has experience with Hushmat installation.
And it's time to look at the engine and transmission mounts! Some of the sound definitely comes through the firewall.
Thanks,
Jim