Q: My E350 is making a loud humming noise but it you can't hear it outside the car.

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My E350 is making a loud humming noise but it you can't hear it outside the car. As long as I stay at a steady speed it fairs off, but when I press down hard on the gas it's like it is straining a little and the humming noise gets louder. There are no lights on to show anything being faulty. I can only hear it while driving. When I lift the hood there are no sounds, the car runs really smooth.

My car has 85000 miles.
My car has an automatic transmission.

Hi There, This may be caused by a couple of different things such as a water pump that may be starting to fail or possibly an alternator that is beginning to go bad. Either of these will produce a bit of a humming or whining noise that will change as the engine RPM increases or decreases. I would suggest having a professional from YourMechanic come to your location to take a look at your vehicle to properly diagnose and repair.

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