Whats that banging sound in my truck?

I have a 1989 GMC 1/2 ton pickup five spd with a350. when I take off it starts to bang the faster I go the faster the bang goes.

What you may term banging another may term as knocking. With a bad U joint, at highway speeds you may experience a vibration in connection with it. Or, when backing up or going at a crawl, you may or may not hear a kind of sqeeking sound.

If you you are sitting still, rev the engine and the sound changes pitch or gets faster, engine, if not, it is drive train or maybe brake or wheel related.

It could on the outside chance, be a hole in the exhaust.

sounds like a drive shaft problum

If it bangs at idle you have a loose connecting rod, if only when driving, it sounds like a common joint coming loose. Good luck.. Junkman

Tell your girlfriend to stop banging inside the bed. Seriously, it may be a driveshaft knocking against something or the exhaust knocking against something. Something that rolls or turns while the truck is moving could be the 1st place to look.

a belt