When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
rattling noises tend to be untorqued bolts...or a miss-installed flange junction. i believe the y-pipe to cat back setup is a flat junction and not a ball joint. climb back under and find the bolt!