i have noticed the past 2 days my truck has been making a terrible sound in the back end underneath the bed of the truck.

the sound sounds like squeaky bearings with dust in them or something but the sound doesn't change its always consistant... so i'm not sure that its bearings.

it only happens if i have a load on the engine like half throttle or more and over 2,000 RPM's. it seems to go away after about 4,000 RPM's.

just wondering if anyone has recommendations on what to look for or what i could do. thx.