Recently I have been hearing a humming noise that increases with speed. I don’t get it when the car stops. I think it’s coming from the rear but only when the car is moving and steadily increases in volume as speed increases and comes down as speed comes down. It’s not coming from engine or transmission but coming from the rear wheels. Could it be a bearing? or both bearings? Is hard to make out if it’s left or right of the windows when the windows are closed.
It is hard to determine which one, It could be a u-joint, differential, wheel bearing or loose exhaust system component. I have the same problem currently at 30 mph and above and am considering letting it go until it is seriously identifiable. Many wrong parts can be thrown at a problem without a proper diagnosis and sometimes it can be difficult. A good mechanic is the first shot as a minor repair caught in time could save a major repair.
To check the wheel bearings, go at a constant speed and then slowly swerve left and right. If the sound changes, increase or decrease, then it is the bearings. If the tires were recently rotated and they have been on the vehicle for awhile or they are directional tires, they could have been mounted backwards and knocked a belt loose or if directional, going in the wrong direction.
My rear bearing droned for a long time, and it did not get worse in turns. To identify the side, find a mechanic who has “chassis ears” (mountable microphones). They isolated mine (1999 E430) to the left side. Repair is not so easy, and it cost me $800 in NJ.
It could be bad tires. Rotate them and see if the noise goes away. My son-inlaw had the same problem and it was tires. New Michelins and he is very happy, but poorer.