gone_fission

Hi all- I have an 03 SL55 that I have brought back from the deferred-maintenance grave which its previous owner dug. I have fixed everything except one annoying problem. When passing through the 600-650rpm range, I get a hum/buzz/vibration. It is most apparent when accelerating from a stop. It occurs in all gears, though it is most obvious when under load in D or R. The vibration is not particularly intense, but it nonetheless is unacceptable in such a vehicle.

I have replaced:
All ABC accumulators and pulsation dampers
Engine mounts
Transmission mount
Valve cover gaskets

The PO replaced the harmonic balancer, plugs and ABC pump not long before he sold the car to me. In addition, I have cleaned out the throttle body and reprogrammed it via the instructions on the W211 forum. Nothing seems to help (though the engine mounts did improve it slightly).

Any ideas?

gone_fission

For anyone suffering from the same issue that finds this thread, check your ABC lines! I did the transverse control arm bushings a couple days ago, and found that there was a rubber ABC line bushing missing in the driver's side wheel well. This was causing the ABC line to touch the metal bracket and cause a persistent buzz/hum around 600-650 rpm. Replacing the rubber bushing caused the issue to disappear completely.

sound 8

I had something similar on my S600, it was the gear box. Try changing the oil, and flush it out beforeyou put new oil in.

Nor Cal SL55

+1 on the trans fluid change

horsepowerfarm

If you have checked the above mentioned items with no luck. Find out if the engine has ever been out of the car. If the flex plate is installed backwards (yes, it has happened) it will setup an annoying vibration at low RPM.