I just bought my first teg its a 97 ls, has aftearket exhaust. For some reason it likes to rattle at about 1000 to 1500 rpms, doesn't seem to be getting worse just don't like it and would like to fix it.

 

check to see if any hangars or hangar bushings are broken.

 

^ or leaks,if anything needs to be tighten, or fell off the hanger

 

Usually it's the heat shields. They rust and become detached from the bolts.

Heat shields are numbers 1, 5, 6, 27, 28, 29. You also have a heat shield on the exhaust manifold.

Hangers are numbers 13, 14, and 15:

 

Like he said, check the heat shields first. Also header heat shields.