Hello, I have a 04 GMC Sierra 1500 CC with a little different sound/problem than normal. Shifting from Park to Reverse there is what sounds like a electrical short followed by a clunk. Then from reverse to drive same sound. The sounds only happen during engagement not disengagement. To add to the mystery the sounds also happens when taking off from stop through 2 gear shift point. I have not heard it at 3rd gear shift point yet. I took my truck to the garage and told them the same thing as above. They thought I was crazy but we found it coming from the rear output shaft of the diff. If you put your hands on the case just infront of the output shaft while someone shifts from park to reverse you can feel something hitting the case. This is what makes the electrical short sound. Does anyone have a clue on what is going on here? For more info the truck runs fine and has been getting worse since purchased 2-09. As far as I know everything is stock mechanically. Thanks for the replies Kingdog

 

How many miles are on the truck? The loud engagement when shifting is likely from worn gears causing too much backlash.
I can't explain the electrical sound... Does it sound like arcing?

 

48k now. purchased it with 25k in 2-09. shortly after purchase clunk started then electrical short sound. yes, arcing is exactly what it sounds like. I'm not going to fix it until I have to but I don't want to grenade my case. unfortunetly free estimates on tranny/diff work are not free.