Rinehart baffles have been known to loosen up over time, especially the older models. They will rattle inside the pipe, that rattle can vary, depending on circumstances.

 

Had something similar....and this may not help......but mine was actuallly a cracked exhaust bracket. The tech (who happens to be my son) took his time and when he took off the bags and grabbed the exhaust one side was loose.....when he took off the exhaust, the bracket came apart. Changed the bracket and no more noise.