I have a chevy avalanche. i have already replaced the transmission. I am getting a squeak from underneath the truck. As I accelerate, the squeak speeds up. When I get to an increased speed I don’t hear it any lo0nger, probably because I am outrunning the sound. Any idea as to what is wrong?
Check the u-joints on the driveshaft.
We have no idea about how many miles are on your odometer, but it sounds like worn-out u-joints.
You will know for sure if you drop your driveshaft while driving down the road.