With a new exhaust setup, how much interior noise is there? I dont want to be driving and have a constant buzz in my head.

 

It's gonna be louder..but not that bad. Check my clip in the V6 Soundclip Gallery
https://mustangforums.com/m_471610/tm.htm
It's at the bottom of the page

 

its not a REAL big difference unless you take off your tips... then it gets LOUD inside!!!

 

It depends on the mufflers you get and how you run the pipes. Dumps are really loud inside the car, but pipies run out the back are quieter.
Also, which series muffs you install. According to Flowmaster, there are no power gains between their loud or quiet mufflers. So you can always go with a quieter muff.

 

I have flowmaster 40s and around 2K RPMs in 1st gear, it's very noisy inside, but that's only when you're pulling out or something. When driving it's not annoying at all.