leak in exhaust gasket

[wav399]

Has anybody experienced incredible vibration and noise from a leak in a gasket in their after market exhaust system?  I am having some big problems with this and the nissan guys say its probably that.  I can even feel it in the pedals.

[WhiteS13]

Had a nasty leak in my other car, and it killed all my low end acceleration.  The car wouldn't idle very stable, because I was losing back pressure.  It also had a dirty puttering sound that lasted for a day because I was too paranoid to drive around like that and get pulled over by cops.  

The problem with my car was that one of the flanges was actually warped, and didn't bolt on flush.  Took the pieces off, and had a machine shop re-surface the flanges for me.  Then went to the exhaust shop, and picked up some gaskets and dabbed a bit of muffler cement on it.  Problem was fixed.