2008 ML320 CDI - droning/buzzing/vibration issue
 

So I'm about to send this car with my son up to the NOVA area where he's moving in a couple weeks. Got the brake booster recall dealt with, got his Android stereo about working (thread coming soon on that adventure), now got another problem.

When driving at about 40-50 mph, up a slight hill, give a little acceleration, I get a raspy buzzing vibration from the back. As soon as I let off the pedal it goes away. It is very intermittent and does not happen every time.

It almost sounds like you're driving over the indentations they put on the edge line to warn you that you're running off the road. Or a car that has had stereo upgrades, too much bass, and no Dynamat, and the trunk lid is rattling.

I lifted the back, got underneath, and nothing looks out of place. CV joints intact, wheel bearings feel good, can't see anything suspicious.

Any ideas?

Sounds to me like a heat shield either loose, or rubbing on something. I have also heard that parts inside a muffler can come loose and make a similar sound. Maybe mount a Go Pro under the car in different places and try to duplicate the noise? Just throwing things out there......Rich

Thanks, I pinged the service advisor at the local dealer and he pointed to the exhaust too. Saw it on another one a few weeks ago.

Update on this:

Finally the car popped a code for wheel speed sensor left rear. ABS fail, ESP Fail warnings on the dash.

Replaced all 4 wheel sensors with genuine MB sensors (sorry got burnt too many times on aftermarket sensors), cleared codes, did the ESP drive test, and guess what, the buzz started decreasing.

Reset adaptations on the transmission and it's now nearly gone.

Wonder if the bad speed reference was messing with the transmission operation and the transmission was trying to compensate for the bad data?

Or maybe the ESP magic was manipulating the rear brakes trying to correct some perceived anomaly in response to bad speed signals?

Mercedes dropped the SBC brakes at some point in the 211, does your later Bluetec have SBC brakes?

Never mind... I see its an ML? Didn't know you had one of those!