Just searched numerouse words and didnt find anything exactly like what I am experiencing. Its a hard one to explain.

I've had a strange "tinny" vibration like noise after truck sits for a while (hrs) and most noticealble at colder temps although I've heard it on a cool AM in summer. It only happens 1st couple minutes and starts from stop...seems to be specific to 1500-2000rpm range so it'll come and go as trans shifts as I accelerate. Magnified when under load (pulling camper from stop or now that I'm loaded down with plow and balast). Goes away after only a few minutes or even 1st start from stop (subsequent stop/start wont do it).

Its been doing it for a few years and 1st thought it was U-joints. I replaced them on the rear driveshaft and the noise persists...

Any ideas?

Could it be something as simple as a belt noise or idler pulley?

I shoulda pointed out that where the noise is comming from...sounds most like under the truck, towards the back. Not positive though.

After looking through more posts...maybe a heat sheild is ringing out when its cold? Sounds like a light gauge metal resonance...

Yeah, could be a shield on the muffler, could be a baffle loose in the muffler

I have been hearing a similar noise on mine also but it sounds like it is coming from under the driver seat or more towards the front of the truck i have tried moving things trying to make that noise under the truck and cant figure out anything either.