So i needed a muffler really bad and decided to have it replaced. I decided I may as well upgrade the rest as well so I had the shop put in 2 1/4 inch pipe all the way up to the downpipe, new muffler and resonator, and removed the cat since it would have been too small anyway. I believe it was like 1 1/2 inch or so before. Anyhow since I did that, whenever i go thru 3000 rpm to 3500 rpm i get this wierd rattley sound. The shop suggested adding a smaller resonator in place of where the old cat was. Im thinking maybe i should just save up and get another cat in there. At the very least I'll get rid of the unburnt exhaust out the back... Any suggestions? Would a cat or another resonator fix this or is it just the pipe size? Oh btw its a B16sir2.