DanielFD

I've been having this weird issue for some time now. Whenever I have my foot on the gas (even lightly) and i go over any type of bump or pothole i get this soft clunk sound from the exhaust in the back. For a little time i had some vibration from the rear because of unbalanced tires over 60mph and it would cause that same sound from the exhaust. Upon inspection i couldn't find anything that could cause the issue. Exhaust rubber holders for the exhuast seems fine and shaking the exhaust while stationary doesn't replicate the issue. Whats weird is it only happens when i have my foot on the gas. Anybody have any experience with something like this?

Yidney

How have you narrowed the sound to the exhaust as opposed to something in the suspension?

mrbobby

I would closely check the rear driver's side spring. In my experience, 208 and 209 coil springs have a tendency to break at the bottom 4" or 5" from the end. It is very difficult to see the broken piece as it slides under the rest of the spring. This condition can result in some strange suspension noises, at least it did for me.

DanielFD

Well, the sound comes only when i have my foot on the gas. But maybe that doesn't necessarily mean its the exhaust making the sound, I'll inspect the rear suspension when i have time and update!

DanielFD

So i did some more experimenting, the sound is definitely from the exhaust and not the rear suspension. It sounds like the engine is surging a bit when i go over bumps with my leg down, but the engine isn't surging at all, it just sounds that way. I think i'm going to go ahead and change the exhaust mounts, maybe there is too much play in the exhaust.

Fatz

I would be surprised if the exhaust hangers are so loose as to cause a change in the engine tone, if I understand you correctly.

While you're under the car you might check the points where your primary pipes connect to the car frame (probably just forward of your oil pan).

Another possibility is a break in your pipe someplace, thou I think you would heard a definite change when just accelerating (medium to hard), if that were the case.

DanielFD

Thanks for the suggestions guys, might be able to take a look under the car this week and will double check all the things you told me about. I have a feeling it might be a break in my pipes.. how can you check for something like that?

Fatz

First you should look for any water under the car, excluding an area at about the center of the car under about where your dash is. Water in this area may just be water from your A/C. There will be water visible only if there is a hole or break on the bottom of the pipe.

You can use a spray bottle of really soapy water and spray the pipes as the car is running. You have to pay close attention and use a lot of spray, as the pipes will get hot rather quickly. Spray along the pipe looking for bubbles as you spray areas of the pipe. It will evaporate pretty quickly. If the leak is on top of the pipe, bubbles will be hard to see.

You can sometimes find a leak by holding your hand close to the pipe. Be very careful, as the pipes of course are hot, and the air that would be escaping could be greater than 250 degrees, depending on where the leak is. About 300-400 degrees near the down pipes and engine to about 175-225 degrees near the tips. The exhaust gas is going to be hotter than the outside of the pipes.

If there is a leak in the area under the car cabin, you may be able to hear a hissing when you press down on the accelerator (window down).

Good luck....

DanielFD

Awesome info, Thanks Fatz! hopefully I can locate the problem!

Fatz

One more thing... for clarity... If it is indeed a leak in your exhaust, the "surging" you mentioned could be due to the change in pressure seen by the engine exhaust, which would suggest an opening at a connect point (weld or clamp), at one of the exhaust components. Since it comes and goes, a hole in one of the components or along the pipe between connect points is unlikely.

So, you don't have to spray the entire length of pipe/s.

(Unless you have had work or mods to your exhaust, everything is likely welded and no inline clamps to check.)

DanielFD

Well noted!! I haven't had any exhaust mods or work done but I'll make sure to take my time inspecting the exhaust. Thanks again.

Shrumsjs

I had a somewhat similar clunk on my 08clk350 and found that the rear sway bar bolt was missing. The colt connects a stall tie bar between the sway bar and the back of the wheel. Was glad it was not the spring as I suspected.

DanielFD

I had the rear sway bar bushing replaced and had all the bolt tightened down a couple months ago. But i surely will check it out. Just waiting for some time to do some work. I'm going to change out the rear diff fluid and i'll be posting about that for sure.

Shrumsjs

I also had clunk sound on my 2008 CLK350 and found the sway bar bolt missing. $10 bolt from the dealer and some locktite fixed the proble. Drivers side rear.

DanielFD

Minor update. i did some work on the car (changed out the diff fluid and steering fluid). so i took some time to find what was causing the problem turns out its most likely the steering rack guard, i had it tightened down as i felt it was loose a bit and the sound is almost gone now. guess it was vibrating when i pressed the accel pedal. what weird is i was pretty sure it was from the back. no idea how i miss judged.