Strange noise from under rear of truck

08 DC TRD - I just went out in my garage to get something and heard a weird "electrical buzzing" noise. I thought something in the garage was running and then I realized it was coming from under the rear of the truck. The truck hasn't moved or been driven in over 5 hours and has been locked the whole time (in case that helps). I started listening in the rear fender wells on both sides and it kinda sounds like a really loud fuel pump in the gas tank if i had to make a guess. As i was listening it suddenly stopped and is no longer making the noise. I've only had the truck a few days and am really puzzled by this noise. Anybody have an idea?

 

Yep.... I think it even states it in the owners manual if i remember... But kinda a weird thing.

 

ok cool thanks, i must have impeccable timing to have went out there during that time. it's normally eerily quiet in my garage so i noticed it right away - i wonder how long it runs for? sure seemed loud!

 

owners manual - that would figure. I haven't had time to browse that yet, still playing/learning with the new rig! Came from a saturn rattle bucket - and i was a saturn tech for years - and i had foam and stuff everywhere to keep the thing from rattling. didn't matter, stupid GM stuff