Unknown Buzz

ok i just got a 1993 gmc jimmy it sat for a year but it runs great but today i hurd a unknown buzzing sound in the back under the car and i have hurd a werr that gets faster what i go fast and and when i break it the werr almost sounds like its winding down (like thows toy cars you roll over the floor a few times and let go) i was thinking the 4 weel drive was stuck on cause i don't remember hearing ne of this be for i turned it on just to see if it worked but u know the noises could have bin there the hole time ne ideas what my problem might be

where is it coming from? is it the gas pump?

where is it coming from? is it the gas pump?

its comeing from inbetween the back tires and i just found out that the other noise stops when i back out of my parkong spot put my jimmy in nutral and turn my 4 x4 in hi then low then off

i dunno. if it is a buzz then it's electrical. if it's a whir or a grind it is usually mechanical. might be one of your bearings.

one last question is it while driving or sitting still? if while driving then it's your rear end. something but not sure what. good way to find out is to crack open you differential and see what is inside. look for filings in the oil. or chunks missing off of the ring gear or spiders. my boss had this happen to his suburban.