[stacy's stang]

I have an '03 GT. My husband has an '04 Mach 1. He just put flowmasters on his (2 chamber). I was not impressed and want something much louder and deeper. So I went to straight pipes yesterday and I must admit, that is too loud for even me. After listening to the sound clips for mustang exhaust, I think I've decided on the Bassani muffler. I read in another thread about problems with the catalytic converters. What kind of problems?