I just got finished putting on my Grip V2 exhaust and I drove the coupe around for a short bit and noticed a few things. It is somewhat droney anywhere below 3k (not really a problem, just wondering if it is supposed to quiet down over time?). Also if I press down the pedal more than halfway (fairly hard acceleration) I get a nasty squealing noise (goes away somewhere after 5k). Sounds something similar to dry belt, the only thing is I never noticed this before the exhaust install, and the stock exhaust was definitely quieter. Also I can slightly hear the squeal (very briefly) when sitting and in neutral and reving, however driving is where I can hear it for a longer period of time.

EDIT: After further testing I believe it is a belt. Exhaust sounds great.
EDIT: This is the non clearance version.

Post a vid of it if you can. Is this one of the clearance exhaust from ARK?

^+1 Was gonna order one of these.

No its the regular, non clearance one. You really have to be in the car (driving) to hear the squeal.
I can get the squeal pretty much in every gear but first, so long as the pedal is almost to the floor. (60-80% throttle)

Re-check to make sure there are no leaks. I didn't tighten one bolt on the cat and it was a lot louder in the front and raspy. After securing/checking all bolts, the Ark sounds great.

^^^this...also check for exhaust leaks. It happens where the weld isnt the greatest and the added pressure causes it to crack.

I think it's a belt. I went back under the car today, rechecked all the bolts. Then I realized it had been 70* outside and I was running the car with the air off for the first time in a couple months. I tried to hear the squeal and I couldn't.

On your install was your mid pipe flange hitting against the 3rd member? mine was but I adjusted it today and now it's sitting about 1/8" away.