Lately I've been hearing a rattle sound comming from my exhaust. Got under the ram this morning with a hammer and tapped my Magnaflow highflow cat (99069HM). Sure enough it rattled.

Heres my issue though, that generally means my cat has seen better days. But this cat isnt more than a year old. Also, after a few seconds of idle the rattle goes away completely, tapped the cat again and there was no rattle.

Im confused on what to think. It cant be exhaust clamps because its welded. Ideas??

 

My magna-flo cat does the same thing.

 

the heat shield may have a broken weld. my thunderbirds heat shields on the cats had broken welds so i put a couple big hose clamps around them and they shut up.

 

haha theres a heat shield? i dnt think theres a heat shield on the cat but ill def check

 

if you look at your cat you will see a space between the outside and the inside with thin sheet metal on the outside. that thin piece is the heat shield.

it might even be as simple as there being a rock in between the heat shield and the cat and when it heats up the metal expands and holds the rock tight enough to not rattle.