eltigre90

hello, im hoping someone can help...my wife's 99 c280,140,000 miles, has developed a "moped"-like sound from what seems to be behind the dash/radio.....happens once car is warm and speeds up and slows down with respective accelerationand deceleration...thought it was the center bearing so i replaced it( needed a new one anyway)...pil and tranny fluid levels check out fine....cannot hear it if car is parked and accelerated......started out of no where...drive shaft u joint seems fine...flex joints and tranny mount are pratically new.....any help will be appreciated,,,thanks in advance! took out A/C control to better hear the noise....oh, and it doesnt matter if the A/C is on or not..,,(tried to upload video but cant for some reason, sorry);..its only heard from inside not outside at all

cgshawaii

1. The alternator can generate radio frequency noise and there should be a capacitor on the voltage regulator to control this.

2. Since you report the noise happens when the engine is warmed up, perhaps the engine cooling fan is slightly cocked and rubbing against something, or something is loose and the fan is hitting it.

3. Engine warm, hood up, get in there and use your ear to find a closer, better description of the noise source. AC should be off, or report whether the AC on or off makes a difference. We need to assess whether the noise is AC, engine fan, or something else.

eltigre90

Thank you for the reply! I crossed posted this a bit back but didn’t update on all, sorry....it wound up being the insulation around the driveline tunnel around the front flex disc; it took on some water and started sagging onto to flex disc.. took it out and gone was the noise