I have recently aquired a squeak in my truck, but only in gear... It's vehicle speed related, not engine speed. I noticed it when backing up (it does it going forward too though), and as soon as I took it out of gear and started coasting the squeak quit. I'm going to see what I can figure out in a couple minutes when I go put my tailpipe back on (), and I'd appreciate any suggestions. I'm thinking maybe a bearing in the rear differential, but I'm not sure. I have absolutely no experience with differentials, so you'd have to walk me through what each part is like a noob. I'd like to do this myself if possible. My only other thought is some part in the transmission.

Luckily I just got my first year of college paid for through a scholarship so I'm not completely broke.

 

You could have a u-joint in your drive shaft going south. Do you do heavy pulling, or burnouts? I would check and see if you have any movement in your drive shaft (get under the truck and shake the bejesus out of it). A tight joint will squeak also.