Weird sound from exhaust
 

Did some cleaning of my TB and intake. I put it back together and started it up and heard a weird sound (Reminds me of when people spin the wheel on the price is right) coming from what sounds like the cat. Now this happened when i first put it back together and drove it around and it stalled game me PC0300 (multi mis-fire) and didn't want to turn back over. It went away after if warmed up drove about 20 miles was fine, drove to work about 20 miles was fine, then drove home again about 20 miles was fine until i came to a stop light and started making the sound again and tried to stall, so i pulled off the road and let it sit for a while, so i wouldn't contribute to a traffic jam, and picked it up later... When i picked it up, turned it over it started making the sound again, drove when i took my foot off the gas it got lower pulled up to a stop it was pretty quiet. Still was there though, pulled up to another stop light gunned it to about 3k rpm and it was gone. Is this just my intake dumping loose carbon into my cat and clogging it up? and i just need to burn it off by taking it on the freeway and pumping out some RPMs? Also i should add that i have a 1996 Cadillac Eldorado. Thanks.