If the knocking is when you hit a bump it could be your axle hitting the frame, or you need shorter swaybar links.Make sure your pinon angle is correct or you will were out your drive saft u-junts.
The air bag rear suspension on your vehicle has failed. This is an expensive repair.
Your suspension is probably shot. Check your shock absorbers.
I am looking for a bushing part I think but I am unsure where you can get these can anyone help me?
u knocking on it
The rear differential is a part of the power train, not a part of the suspension on a vehicle. It is the suspension system you need to be investigating on your vehicle. You more than likely have a broken spring.
I would check the suspension bushings, if one of them is worn it would cause a knocking noise.
Trucks - 1999 Rolling Thunder Part 7 Independent Rear Suspension Install and Upgrade was released on: USA: October 2010
Some part of the rear suspension is worn, bent or broken.
possibly worn shock absorber rubbers,loose mounting bolts,broken mounts. more info needed to diagnose
You talking bout control arms or the rear tie bar?
No, it is on the axle of front wheel drive vehicles and some rear wheel drive vehicles (if they have independent rear suspension).
Independent rear suspension.