Sometimes when I back up my truck makes a grinding sound that kinda sounds like the sound if you leave the emergency brake on. Seems to happen more when it is cold this sound comes from the back of the truck. Has this happen to anyone else and does anyone know what this sound might be? I have a 07 Fx4.Thanks.

 

I just talked to the service manager at a Ford dealership and he said it also does it on his 07 Fx2 and he was told it was normal but could not tell me what it was.