190E strange sound in reverse only

[crhenkel]

My wife's 1990 190E 2.6 started making a metalic sqeal last week. I am getting a strange sound from the front wheel wells but only in reverse. At first I thought it was the front brake pads wear indicator. I have been expecting the front brakes to need attension soon so it seemed likely the pads were just worn. But it only makes the sqeal in reverse. It is a high pitched metal squeal noise and I can only hear it backing out of my long driveway ( or other times in reverse) Rotors are smooth and seem in good condition. Pads appear from initial inspection to still have alittle life left in them. What could this be? Help!
I do not know much about the parking brake set up on this car, could it be something in there handing up?