Where do I start to troubleshoot a noise coming from the rear of my truck.

Is the noise from the brakes? Rust builds up on the rotors overnight, and the first couple of times you hit the brakes you will get some grinding. The brake pads where off the surface rust. After that, the noise would be gone.

I had the brakes changed,emergency brakes changed and had the rear end checked out and I still have the noise. It makes the noise like every rotation of the tire you hear a little knock,and it will do this for about 200feet than I won’t hear it again till the next morning after it sits up a while