At about 35k miles I started hearing a "Ping" noise when my truck shifts from first gear into second gear. This occurs only after the truck has sit for a bit (driveway or parking lot at walmart etc.) After that first shift it doesn't do it again, (after stoping and starting at a stop sign etc.) It's coming from the front area of the truck. My instinct tells me it sounds like a U joint.....but odd that it only does it once after the truck sits for a while. Had my transmission fluid changed today at the dealer as well as all Diff fluids and transfer case (now has 45k miles) Dealership didn't know. Any ideas?