I just had some magnaflow cats installed on my sierra today, I was just wondering what the crackling sound was when you turn off the truck. Is it normal. Any info. will help.

 

magnaflow cats have been known to fall apart, performance cats they ain't.

That crackling is probably just from them settling, given they're new and all. It could also be from air getting sucked back into your exhaust from the restriction caused by the cats.

 

Haven't heard good things about these cats.

 

it the cooling effect when you turn off your truck and things start cooling down....