Car has been running good for years nothing but oil/trans fluid changes and tires this noise has appeared. Car still seems to be running fine intermittently comes and goes u will hear best when car stunts off

 

Sounds like your ABS pump is on the way out. Normal failure item on the w211, it's called SBC or something to that effect, it pressurizes the reservoir and makes sure you have brake pressure all the time. In your case i'm surprised you don't have a brake warning light on, it sounds like it's not holding pressure and causing the pump to run constantly.

 

Bump any other ideas about the video I posted ? My brakes seem to be working fine.

 

Get an automotive stethoscope and pin point the noise.

 

I'm having the same noise right now. It definitely seems to be coming from the SBC. Brake fluid level is normal.

OP, did you ever get to the bottom of it?

 

Could be the pressure resivour is going on the SBC unit.

 

That sound is coming from the auxiliary water pump. It sits just behind the passenger headlamp and pumps coolant from the radiator into the heater core for the climate control. In the video its what you see at the 34s mark with the wire harness plugging into it. You can see the hose running by the sbc. Touch the hose or pump when you hear the noise next time to confirm its that as the vibration will match the sound.

 

That's great news! I'll check that out tonight. Thanks for the info.