My truck is a 1991 k1500 (4x4), got about 189k, a 4.3. my truck likes to make this loud scream at about 50mph... but only when im on the gas. I can go as fast as I want(with the noise going) and as soon as let off the gas the noise goes away, then comes back when i hit the gas again. Also the noise seems to jump if it let off the gas quickly. I am not familiar with the mechanics of a 4x4 but I am hoping it is something that I can fix myself. One friend said that it was my throw out bearing but another said it sounds like a bad pinion bearing. whatever it is it really isnt affecting the truck, i still drive it and use it for dump runs and hauling my mower but i would really like to fix it. Thanks for the help!

 

First I would have it serviced,making sure all gear boxes were checked. Then I would jack it up to see if you can duplicate it sitting still so you can get an idea of where it is. I doubt that it is release brng. I had a rear trans seal do this one time.

 

I have put the truck on jack stands and run it and using a stethoscope it sounded like it was coming from the rear diff, but also sounded like it was coming from the trans but was louder at the diff... not sure if this helps, and i really do not have the money to have the truck serviced professionally

 

What I am getting at is make sure something hasn't ran out of grease. Try squirting some oil around pinion seal.