just like the title says i have a weird driveline noise that started about 500 miles ago, truck is an 03 chevy 2500 hd duramax/allison 4X4 ext cab short bed with 49,000 miles on it. there is a weird squeak/creaking noise coming from the rear of the truck( right at the back of the cab... i think) in reverse and it does not do it in neutral(rolling) but does do it when i back up in reverse it also does not do it in drive in gear under power but will make the noise at low speeds when i let off of the gas and coast. the noise increases speed as the vehicle increases speed. i have been under it and cannot see anything touching or rubbing. it might have been doing it for a while now and i just didn't notice it because it just got warm enough to roll the windows down here and that's when i hear it. it is driving me CRAZY!!! thanks for any help and by the way this is a kick ass site.

squeaking or creaking noises from the driveshaft usually come from the ujoints.

they are not greasable correct? so i would need to replace them? how much does that run?