2008 C350 (not 4matic)

Just started getting a strange noise and it's making me uneasy. The noise is very low, sounds like it's located somewhere along the middle of the car either right next to the driver side (under the center console) or behind it towards the rear seats. It's hard to tell exactly.

Noise sounds like a low hum grind (not grind per se, just not smooth). It sounds like it could be something spinning also. It's hard to hear but I only hear it 1) when I'm driving 2) when I'm not accelerating 3) more noticeable 5-20mph. Car seems to drive fine other than this. Sounds transmission related, going back to the rear wheels maybe? Any ideas?

UPDATE:

The noise is super hard to hear right now. I never noticed it before 2 days ago though.
It's speed dependent, not RPM dependent.
When I'm driving with the gas on, can't hear it. When I take my foot off the gas I can hear it. If I put it in neutral I can still hear it.
It's kind of a low, gritty-ish noise.
I originally thought it was coming from middle of the car, in between front and rear seats-area. I'm not entiresely sure now as it's super hard to pinpoint. Driving with the windows open doesn't help either as I cannot hear anything out the windows.

 

I'm trying to use the search for this issue and not coming up with much for w204s...

But... can anyone tell me what the symptoms/signs of a bad center driveshaft support/bearing are ?? Could this be it?

 

You have to visit a repair shop, there is no other way. The transmission is located somewhere around there but that's the worst scenario for you because it is expensive to repair.

 

There has to be a way to trouble shoot, or at last narrow it down. I'm hoping someone has had a similar issue. I've been reading on the forum of people with other models and similar sounds and I'm good with a wrench and have access to a lift, just looking for some help troubleshooting. Hoping it's not the transmission - car seems to drive fine except for the noise, which comes and goes.

 

If you have access to a lift, then your best bet is to get the car up on the lift, with one person in the driver set, another trying to pinpoint the source of the noise. But to try and "troubleshoot" it by posting descriptions on a forum, sound can be very deceiving when it travels through several layers of different materials (metal, insulation, carpeting... etc). Any suggestions you might get here are going to be pure speculation.

 

No vibrations like a flex disc going bad, just noise ??

 

Is there any way it could possibly be an issue with one or more of the tires, like a belt maybe starting to separate? Or does it sound like more of a mechanical type noise?

 

Probably going to be doing this soon.

No vibrations that I can tell, just the low gritty type noise. from about 40 to 70 I can't even hear it at all.

Tires are new. Can't hear it with the windows down and it sounds drive train related (middle of car) but it's honestly super hard to tell so I'm not 100%.

Thanks for the help though. I know it's hard to diagnose a noise on a forum but I was just hoping maybe someone on here had something similar happen who could chime in.

 

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