4 Wheel Drive/SUVs: 97 Z71 squeaks during acceleration, drive shaft, support brace

Question
I have noticed a squeak coming from the middle to rear of my truck.  It only makes this noise if the truck is in Drive. It gets louder and faster during acceleration until disappearing around 30mph.  I got underneath the truck and shook everything, nothing.  I got on the back of the truck and jumped up and down and nothing. which is how i figured out it only does it in Drive because i immediately got back in the truck and put it drive and gave it some gas and it made the noise again.  I got back on the bumper and jumped, nothing again.  Any ideas?

Answer
this will be the center support bearing on the drive shaft Jason! I am 100% sure due to having the experience myself. In the center of the drive shaft there is a "donut" looking support brace bolted to the frame, this is the bearing. You have to take the drive shaft out and seperate the two halves to repace the bearing and this WILL fix your truck

Matt