Have a 2004 Silverado 2500 (not HD) 4X4 with Quadrasteer and 91,000 all highway miles and very little time in 4 wheel drive. I have a speed related thumping noise from the drivers side front end. Thought it was a tire or hub bearing. Had it checked out by my trusted independent repair facility this morning. Nothing wrong with the tire, hub, brakes, etc; but it appears the differential itself is going bad. Still waiting for the final analysis and potential cost impact. Anyone else ever experience this problem and if so what it cost to repair??? Cheers, Steve R.