Hi. I have a 2010 Sierra 4x4 v8 Single Cab Long Box. Lately I've been hearing a knocking sound in the rear which i first thought was my receiving end. After checking this I still heard it and figured it was another spring snapped - also not the case. Now I hear it when going slowly over dirt road potholes and rocks. When I had it parked yesterday I started shaking/rocking the box back and forth left to right and the noise was very loud around the right rear wheel but strangely not sounding like it is in the wheel. I'm taking it to the shop this week but just wondering if anyone has any ideas on this issue - also checked th lugs and the tire (as well as the spare tire and exhaust) are all tight. Thanks.