There must be a break-in period with the Perrin? I had it installed last Wednesday and it was LOUD. I put a hundred miles on the car between then and Friday, then I took a 4 hour trip up north - near the end I was getting mildly annoyed. I put a couple hundred more miles on it up there, then I just traveled back 4 hours today and there was a pretty big difference. I didn't notice the drone at all. In fact, cruising between 75-80mph, it sounded a bit like the stock exhaust - as in, nothing.
Exhausts must need some burn-in, I guess. This bad boy is a keeper.