Hello all. I havent been on here in some time and my car usually sits in the garage up here in Denver. I drive it once or twice a week. Last month I was driving home and noticed this metalic sound increasing as I accelerated and decreasing at deceleration. I took the car into Firestone and asked them to check the U joints and they said the front one was loose so I had them both replaced. First off I have an aluminum drive shaft that was replaced back in 98 with the TSB from GM. This one had 2 different shaped U joints and they ended up just having to match them at the parts store. I am hoping this was not a mistake? So after 6 U joints the noise is still there, only louder? They have no idea what it is and neither do I? I does seem to get louder under load and at about the 4th turn of the DS. I have 410 gears. I am about to pull off the diff cover and do a diff service just to see whats going on. Am I looking at a new ring and pinion? Dealers are saying 800 -1500 to repair this? Thanks for any help.

 

See if the slipyoke splines are loose.
Look for worn out suspension bushings that could affect axle's pinion angle. Inspect the crosspin in the differential carrier for looseness.
Possibly excessive ring/pinion backlash.
Has the driveshaft been dented? possibly out of balance
loose sheetmetal, etc. clanking?