The other day my 01 ls started to make this rattling sound from the rear of the car, muffler area, and the other noise is a raspy sound from near the middle to front of the car...

I had a buddy of mine take a look and he thinks that i might have a leak in the cat. seals (i guess-not sure on term here) and the leak is causing the rattling in the muffler..

I was wondering if anyone can concur with him or have any other ideas at what might be wrong. Thanks for any help...