I haven't been under my AV yet as I just got it a couple weeks ago but I know alot of time U-joints have greese zerks on them. After market ones for sure but I thought on the larger trucks GM put them on the U-joints that would take care of any squeek from them if it is a U-joint. I can't say I have every had one fail like that. It has always been the klunk that happens when shifting from drive to reverse or park that is caused by the slop that a bad U-joint will create. If you do end up replacing a U-joint. It's not that hard of a job and I would highly recommend getting one that has the greese zerk. It may cost what an extra $.50-1.00 but they last longer. I know my blazer didn't have the greese zerks and when I replaced the U-joint I went with one that I could lube.