I had magnaflow high flow cats (94306 i think, the quiter ones) installed awhile back and shortly after my motor blew so today is the first time ive gotten to hear them. I have stock exhaust other than these and i can hear them when the motor revs. Is this normal or do i have a leek somewhere?

 

shove something in the tail pipe(s) or have a friend block it off and crawl under and have a look see while its running.

 

Describe what your hearing. Paper flapping? Hissing? a rattle?

 

Sounds similar to an exhaust leak but its more audible with engine rev which makes me think its just how they sound. I just wasn't sure if I should be able to hear them through the floor board.

 

Sounds like it could be a leak by the manifolds more than cats. You shouldn't even be able to tell they were changed if installed properly.

 

Alright im thinking a leak where they installed them then, i just had a new motor put in so the manifolds should be good.

 

x2 manifold leak.

 

how could it be the manifold though? I just got the truck back yesterday from having new motor installed.

 

^ There you go. Heat! Expanding and contracting of the manifold due to EGTs, may cause a leak. It is worth looking at.

 

x2. Possibly check the gaskets, make sure everything is tightened down properly.