With as many squeaks and rattles as there always are in a Fox car, I gave up on the idea of trying to keep mine quiet.
FWIW, Frankenstang has a Dynomax Super Turbo cat-back on her '86 GT 'vert. It sounds about as mellow and tame as you can possibly get, especially with the stock four-cat H-pipe ahead of it. However, as stated, it's kinda nice to be able to actually hold a conversation (even with the top down) without having to scream to one another just to be heard.
What, are you kidding me? This is my only peace and quiet! It's worked with every girl i've had in my car that won't SHUT THE HELL UP!

When i can't hear her naggin, it's as good as no naggin at all
