Why do It sound like the back tire rubs but it's not

The possibility of it been your brakes can not be disregarded just be cause the noise occurs without brake application. Obviously, without seeing or hearing the vehicle, I can only make wild guesses. But, a Brake Backing Plate could have been bent and is now rubbing. If Brake Pads were replaced, but installed over the old rotors. Brake Rotors do wear with the pads and develop "Lips" around the edge. Now the pads have worn to a point where the Brake Pad Backings are rubbing on the "Lips" on the edge of the rotors. There are numerous Brake related issues that could cause your rubbing noise. I would recommend you have a shop (preferably, one that specializes in European or Mercedes Vehicles) take a peek. Even if it something simple, it's worth the peace of mind.