ThisIsMe

I have a 2002 C320 wagon and it just started making a hum sound that appears to be at the driver rear wheel.
The sounds is like an electric motor running at a high rpm. It starts at 45 mph and doesn't not change with the speed. It will continue even when the car is stopped and the sound will only stop when the car is turned off.
We kinda tested it and it will start at 45 mph but only when the A/C is on.
I have no idea what would be in that area that could even cause this sound.
Any help would be appreciated.

Carsy

Under some circumstances the direction of where sound is coming from is difficult to pinpoint.

It is not associated with the drive train if it can be heard when the car is stopped.

I wonder whether it could be either the A/C blower fan ( try varying it ) or the engine fan running because of the AC being on. Open your bonnet to find out at standstill.

Let us know .You do not say where you are from in your profile.

Glyn M Ruck

Fuel pump is a distinct possibility. When last did the car have a new fuel filter?

ThisIsMe

Sorry for the late reply. I finally got around to fixing it. Thanks everyone for the help.
I had some trouble recreating it for a while but on a long trip found out the hum was from under middle of the back seat. With the help of people here figured that the hum was the fuel pump and that it was probably working overtime due to the filter.
So I replaced the filter and everything is running great.
Thanks again.

Glyn M Ruck

Great - Thanks for letting us know!