Has anyone had any experience with stock exhaust pipes rusting out in certain places? I've been under the truck and they seem solid.

Getting a rumbling (almost a back flow)when the rpms come above a 2500.

The noise seems to come before the Cat. Could it be that the Cat is partially plugged and restricts the exhaust flow or, is there a stock pipe before it that has been known to rust out?

Any help would be appreciated.

 

Would having a rebuilt engine cause the exhaust to be louder?

 

I have holes in my exaust in the muffler and on the top of the tail pipe right before it is visible thats the only places i know of holes forming.