I currently have FI high flow cats and their stainless steel round style exhaust. There's a lot of vibration that comes into the car and has a tendency to shake the plastic panels in the cabin (causing rattle when reving from a standstill). Do you think I should have flex pipes welded in to alleviate some of that vibration from the exhaust, or will it not help much?

 

I know this thread is old, but would Flex Pipes actually solve the low rpm vibration issue especially under load?

 

Are there no flex sections in your Y pipe?

 

In the stock y-pipe yes, but FI uses an x-pipe