Heat shield is a good place to start, typically that's the case, but on some occasions the Cat has broken internally and will cause a weird rattle vibration noise. Tap around with a rubber mallet to check the heat shields hell the whole exhaust for that matter, but if you cannot find it, then pound on cat and listen. . .
White gauges and Temp Cntrl, OHCw/Buggman LED mod,
Bosch +4, Accel Coil Pack, MSD6AL, Walbro, HiFlo Fuel filter,
Custom Ram Air, K&N, Ported / Matched intake, JBA 9mm wires,
Tweeked FPR, EBC 6k's, DynoMax-S CatBack, Jet-Chip, Reflex shocks,
New Anvil Mounts, Timbren's, Optima Yellow, DB 220A Alt. w/4g. jumper,
Western snow plow, More2Come