My New/old 88 EFI makes a weird sound when i let off the gass and im still in gear its sort of like a deep weeeeeeeeeeeeeerrrrrrrwwwwww and it only does is when im in gear. Its rusted pretty bad but i need to fix this cause its drowning out my sound system!

My 93 does same, does it come sound like its coming from the middle or the rear of the truck?

I was told mine was coming from my t-case, i dont plan on changing it though. I may sell soon

motor or tranny?check replace fluid maybe upgrade to synthetic should quiet things down and run smoother unless you have a trans problem, check linkage stick right.

My toyota was doing the same thing, the rear end ended up messing up, then i pulled it out put a new one in and the noise went away.. the teeth on the rear end were pretty chewed up was thinking that was making the noise