Help!

Car makes annoying rattling noise now. Cant find where its coming from but really sounds like its coing from the driver side cat. I have pypes violator catted x pipe I've had it for 4+months. I have no o2's i recently plugd the o2 wholes with just plugs not o2's to quite the car some. I let the car idle for a while to see if anything had changed and it idles fine. I got on the beltway and the car drives fine with the exeption of the noise. Sound like loose change in the exhaust only hear the noise between 1000 to 2000rpms, accelerating from stops and coming to a stop but when cruising the noise seems to go away. WHAT IS THIS!?

Research says it may be my exhaust shield. So we'll see as soon as i get off