Just picked up a 2002 c240- I've gone through a lot of the car picking up some maintenance slack the previous owner neglected. The one in particular that has me scratching my head is the fuel system. I knowingly bought the car with a loud hum coming from under the rear passenger seat. Also noticeable outside of the car. So I went ahead and bought a fuel pump before doing any kind of digging (taking seat out or putting the car up on a lift). Once I got the pump in the mail, I took the seat out and noticed the hum/vibration coming from the driver side of the car, where you find the sending unit. Despite knowing where the noise and vibration was found (driver side), I went ahead and replaced the fuel pump on the passenger side of the vehicle. Hoping that somehow the old pump was causing the issue. After install, same issue. Hum/vibration... I then put the car up on a lift and noticed that the fuel filter was having the same symptoms as when I listen and place my hand on the top of the sending unit. The fuel filter was shiny and new with new clamps. I then spoke with the previous owner who confirmed that the fuel filter had been replaced a week prior to me purchasing the car. I also got in contact with the mechanic who did the job to verify the work done. At this point I removed the fuel sending unit from the tank and had a friend turn the key to the "on" position (not turning the car on) to run the pump for that one sec. Hum/vibration was def not as severe with fuel sending unit out of the tank but still noticeable. There is also no noticeable motor attached to the sending unit. I have done a lot of searches through mbworld threads and other forums but no one states that a fuel filter or fuel sending unit has made noise, they just seem to replace fuel pump and vualla! Problem solved. Could a fuel filter or sending unit cause such annoying noise? Im trying to avoid the obvious, spend money on the wrong part. Again... My apologies if I am stating anything obvious to you veterans but any feedback would be greatly appreciated-
Cheers

 

Welcome!

Does the car make the same noise while driving?