ive got a 97 lt1 dual cats passenger side cat is rattling like crazy at idle and a little when driving, i checked the brackets and it is not loose, i have a stethescope and it sounds like it has a rock bouncing around in there. is there something in the cat that could break loose and do this? i dont know how anything could have made it through the valve train without breaking something and the engine runs and sounds normal.

 

just a quick one. but are you sure it is not the heat sheild on cat. or on the top of the cat rattleing on it? if it is rattleing on the top of it it will sound like something beating around inside of it...

 

my gf's car had the same noise, it was the heat-shield

 

If it's not a bracket or heat shield bouncing, it's probably part of the catalyst honeycomb broke loose inside there.

I had it happen and it sounded like rocks bouncing in a coffee can.

 

Yeap, pretty common if your car has some miles on it. Just sold a minivan that made that same noise.

 

i found a busted off spark plug in one b4 from when we did the RE & RE abd busted off the plugs to make it easier lol but b4 that tha heat sheild on the underside of pass. side floor rattled like a biatch and took me 2 seasons to figure it out

 

Jack the car up and check it out. Hopefully you just dropped the heat shield. A defective cat can be costly and more difficult to replace.

 

hit the cat w/the ball of your hand . if it rattles inside ...time for a new cat.