New 3.73 Gears, Need Help!

I recently installed a new 8.8 rear-end that had been upgraded with a set of 3.73 gears. I bought them from a friend who didnt know much about it. Everything looked and moved fine until i noticed a "whine" when driving and when driving in reverse, i hear a clunking sound. Im considering overhauling the differential but I want to see if anyone has any opinions as to what to do. Any suggestions or concerns would be much appreciated!

Honestly i didnt...i bought the rearend as whole peice (axles and all) so i assumed everything was done right. I never considered the U-joint. I realize the amount of possibilities there and i appreciate the help!