Have you installed new wheels lately? I had this same problem in forward and reverse when I installed aftermarket wheels with new lug bolts. One of the lug bolts was about 1mm too long and was contacting the brake assembly. I filed down the end of the offending bolt to fix the problem.
Naturally, Benzmac figured out the cause of the problem in about 3 seconds after I had been searching for a solution for hours.
Bill Wood - Webmaster