I have had this slight grinding/rubbing noise in the rear of my 2008 Chevy Silverado 1500. At first I thought it had something to do with the drums rubbing on the brake shoes because it would only make noise in a pattern (as spinning), but I took them off and ran it in neutral and the noise was still there. My guess is differential bearings but I am just not sure. I would appreciate some help with this thank you