See video:
I have a weird groan on startup followed by a whine similar to but less pronounced than an ABC / tandem pump pulsation damper whine. Important to note that I replaced the ABC damper 3 years and 30k miles ago (give or take). Could the damper have gone bad again??

Because of this, and being able to rule out the damper (I think?), I thought the pump was going but I am reading good pressure and the rodeo is performed flawlessly.

I tried turning off the climate control to isolate the AC compressor: no change.

The car was not doing this when I dropped it off to get bodywork done 1 month ago. Not sure how something like this can happen after sitting. Coincidence?

 

I have a similar sound on my 2007 CL550 that I believe comes from a worn/damaged AC compressor. I get the groan/whine on startup, and also a subtle whine at 1400 RPM when the AC is working hard. Turning off the AC stops the 1400 RPM whine. Starting the engine with the AC off also changes the duration of the startup groan/whine (only makes the groan/whine for half a second on startup then abruptly stops the groan/whine; maybe the AC clutch is briefly engaged in startup).

You could try shutting off the car with climate control off, and then starting it up after a few minutes (while the climate control is still off). If it’s the AC compressor, the duration of the startup groan would be reduced with climate control off, and it would stop abruptly.

 

Thanks for the response. I also suspected this early on but the groan persists even with the AC off. Also my whine is at 2000RPM. Have you taken any other action to confirm that it is the AC? I will see if I can get some test info on the compressor from my scanner. I can on other things like bars of pressure on the ABC pump. I will pull it up and see what metrics it measures the AC compressor by and try to determine if my pump is tired. I suspect it may be as I’ve noticed my AC getting weaker recently.

 

For me, the 1400 RPM whine goes away instantly and completely when I turn off the AC (even if I leave the rest of climate control on), so I’m confident at least that is AC related. My startup groan (which sounds exactly like yours) lasts around 1.5 seconds and gradually tapers off when the AC is enabled, but only lasts 0.5 seconds roughly and ends abruptly when the AC is turned off at startup time, so I suspect it’s also AC related, but I’m less confident.

I used to have a slightly louder startup groan, and a whining noise between 1500-2200 RPM. That was caused by a bad ABC pulsation damper. Replacing the pulsation damper eliminated that whine.

 

Is there any precedent for the dampener going bad just 3-4 years / 40k miles after replacement? My ABC pump is still strong (I confirmed through my tests and also took it somewhere with STAR to confirm). It is similar to the dampener noise but not as bad as it was when I replaced it originally.

 

That seems premature for an ABC pulsation damper to fail, but it is something I’d consider a wear item. On my 2012 CL63, it failed in 2020 around 93k km (55k-ish miles) and 8 years age. On my 2007 CL550, it was bad when I bought it this year (neglected by previous owner) and I replaced it right after buying.

 

Mine was also bad when I bought it so I never got a chance to hear the progression of the noise leading up to it being really bad. Because of that it makes it hard for me to say if this noise is that but in the early stages.

 

If you shut your car off, and then start it again within a few minutes is the groan quieter?

My car had run within the last half hour before recording this video, so I don’t think it revved as high during startup as it does on a cold start. The slight groan in my recording of my car is much more subtle than yours, if I can even call it a groan, though it is more noticeable on a fully cold start where the RPMs briefly flare a little higher.

 

Yours does sound quite a bit more subtle and I don’t hear an abrupt end to the groan like mine does after a few seconds.
if I shut my car off and restart it immediately say <1 min there is zero abnormal sound. So it must be fluid related because of the way something seems to need to “settle”. But like I said I have to restart it IMMEDIATELY to get no sound.

 

With mine, I only get a noticeable startup groan if the car has sat for over an hour. If I restart within half an hour of the car being last run, it sounds like the last video I uploaded. I recorded a couple more for reference.

The first video here is a mostly cold start (I last ran the car just over 3 hours ago), with the AC enabled. There is a noticeable groan that lasts 2-3 seconds after startup, and it’s not too different from yours. If I turn off AC before doing a cold start, my startup groan only lasts half a second and ends more abruptly.


This second video also has the AC enabled, but it was recorded 5 minutes after I shut the car off. It sounds identical to the daytime video from earlier today, without much of a noticeable groan, though it also may be in part related to the engine not revving as high to warm up the cats.


If you do a cold start with climate control turned off, and you still get a multi second groan like in your video, then my guess would be an ABC related noise (pulsation damper maybe). My startup groan used to be louder before I replaced the ABC pulsation damper. I’m letting my AC compressor related noise slide for now as the AC otherwise works fine.

 

I did some more digging in mine seems to be unaffected by the air conditioning being on or off. Ours may be similar noises but different problems I think. I may replace my ABC dampener again just to be sure but it’s only four years old.

If that doesn’t work I will just take it to the dealership for diagnosis. I can’t deal with the noise. So unbecoming of an S Class. Believe it or not I took it to a certified MB tech who told me “that’s totally normal”. What a joke..

 

Yeah, not normal for sure, the whine or the startup groan. My 2012 CL63 had neither, it was quiet as a CL or S class should be. In any case, let us know what fixes it. ABC-equipped C216 and W221 cars are fairly uncommon, so every diagnostic data point is helpful.

 

Will and always do! It’s the worst when people don’t post their solutions. Gotta give back to the community!

 

Today, my 2007 CL550's idler pulley seized while on the road, causing the serpentine belt to melt and shred. Had to get towed to mechanic as I lost power steering (and alternator charging and cooling etc). After the serpentine belt disintegrated, I had no groan on startup, and the engine was amazingly silent overall at idle. I previously had a subtle belt noise from my engine that I was ignoring, the startup groan that sounds similar to your car, and a very subtle/quiet whine audible inside the car at idle that I treated as normal but I felt a modern S/CL should be a bit quieter inside at idle. We'll see if replacing the idler pulley fixes my startup groan when I get my car back, and if my car would remain quiet at idle after the fix.

 

How many miles do you have on the car? Maybe I should consider changing the idler as preventative maintenance if nothing else.

As for updates on my car: I had previously ruled out the AC because the noise does not go away when I shut off the AC in climate control. However, when I was under the car yesterday, I noticed a pretty serious leak coming from the low-pressure line's connection to the compressor. I suspect I am low r134 and possibly oil causing the AC the make these noises. I must not have noticed that I don't have AC because of how cold it's been. When I get the leak fixed I will report back.

 

My car has 151k km, so around 94k miles. I’m not 100% sure if my startup groan is AC related or not, but it’s definitely one of the accessories run off the belt as cold start was silent with the belt broken. I have a whine at 1400 RPM when the AC is working hard that is definitely AC related, as that stops instantly whenever I turn off the AC. My car was very low on refrigerant and AC oil when I bought it, and the AC had disabled itself, but I had the oil and refrigerant refilled when I bought it and it seems to be holding, my mechanic couldn’t detect any leaks and the AC has worked great all year aside from the 1400 RPM whine.

 

An update on my situation:

I had both idler/guide pulleys and the belt tensioner replaced, serpentine belt replaced, and debris from the old belt cleaned up. Car runs fine again (as before), though it sounds the same too now that the belts have been reinstalled (cold start groan included). Thus I can't say there were any real audible warning signs for my idler/guide pulley failure, and my startup groan is unrelated to the guide pulleys or tensioner. Nevertheless, it would be a good idea for folks whose cars are getting up in mileage to inspect how freely their guide pulleys and belt tensioner spin, and replace them if they show any signs of wear rather than waiting for them to fail.

On a separate note, over the past couple months, as the weather cooled, I noticed my ABC pump had become a bit noisier, and in particular power steering was getting rather noisy. My car previously had a whine from the ABC pump most audible at certain engine speeds, but replacing the pulsation damper fixed that 6 months ago. The power steering was mostly quiet in the summer, but got noisier as weather cooled (though the noise would diminish when the car warmed up). The dealer I had my car towed to when the belt broke (that replaced my guide pulleys and tensioner) also noted the ABC pump was noisier than it should be. Today, I inspected my power steering fluid, and saw the level was fine, but the fluid was yellow rather than green. I then flushed out the yellow power steering fluid, and replaced it with fresh green Pentosin CHF 11S (same fluid used for ABC suspension). Putting in the CHF 11S fully cured all my power steering noises; now power steering is practically silent at all engine RPMs regardless of how much I'm turning the wheel. However, I still have the groan on cold start.

Takeaways:

1. Inspect your idler/guide pulleys and belt tensioner, and replace them preemptively if they show signs of wear. Don't expect them to give you an audible warning before failure.
2. A bad pulsation damper and incorrect power steering fluid can both cause ABC tandem pump whine. Check/replace these first before replacing the (costly) pump. For me, replacing the pulsation damper (in the summer) and putting in CHF 11S in the power steering system cured my whining noises from the ABC pump.
3. I'm still not sure what causes my startup groan - maybe the AC compressor, maybe the ABC pump, maybe even the alternator or water pump (but I doubt those). I had no startup groan when starting without a serpentine belt, and replacing the idlers and tensioner didn't fix the groan, so it's definitely one of those four belt driven components making the noise. I'm leaning towards the AC compressor being the culprit, but I'm not certain.

 

All-

As suspected, the problem was in the ABC system. I had forgotten to change the rear accumulator when I changed the front accumulator and pulsation damper.

I was led to this conclusion when I was going through parts in my garage and found the rear accumulator that I never installed!

Cant believe that Indy said the noise was normal. Wanted to make sure I closed this one out all this time later!