well, since the day i had my apex-i N1 muffler installed on custom cat-back piping there has been a very annoying rattle from 2800-3200 rpms. Initially i thought it was the carsound cat that's internals were F'd only 6 months after buying (there was stuff rattling in the converter. I had a muffler shop gut the cat, which didn't help, then they removed the heat shield on the cat itself, and then the heat shield above the converter all with all fixing the problem. As a final means of action they cut out the converter and i ran a straight pipe which = loud as hell and rattled like no ones business. all this work was done back in february, and in april i had the same muffler shop install a resonator (cheap ractive straight-through design), which cleaned up the sound of the exhaust but the rattle was still going on in full effect. fast forward to yesterday, i found a local shop that sold magnaflow stainless steel resonators, and had one added to my mid-pipe right after the header for a total of 2 resonators on my exhaust . The magnaflow resonator completely removed the rattle and quieted the muffler considerably, producing a deep sporty sound to the exhaust . There's a lifetime warranty on the magnaflow resonator just incase it craps out on me, although it shoudn't with stainless steel meshing along the inside of the tube. sorry for the long story, but i have posted threads about fixing an exhaust rattle and seen many people posting requesting help.

short version: magnaflow resonator fixes rattle completely and gives exhaust nice deep tone