transmaster

You should have seen the 4.6L they did up on HorsePower TV. It was in a Mustang Cobra. they installed a supercharger, headers, X pipe exhaust and came out with 485 hp. then they started to change out the drive pulleys with ones smaller in diameter when they got done with this and after which they hit the engine up with a programmer the had 585 hp.

NexTGeN

Yah, more than likely its the exhaust manifold.
Over time they might just need to be re-torqued.
If its got somewhere or close to 100k, its probably cracked.
Not a really massive deal, just sounds like crap.