I had the same issue. Got rid of it after 1000 miles. Even with -30dB ear plugs in my ears were buzzing any night I rode it. I communicated with Arthur (the UK agent for the exhausts) and a chap at the GPR factory who made me a one off Longer baffle for the GPR stainless. I have it for sale if you want to try it. It did reduce the sound levels but I'd had enough by the time I got it and had already decided the exhaust had to go.
20.00 delivered for the longer baffle.
If you want to PM me your email address I'll take some pics of it and forward them on.
After going back to the original can, I didn't notice any performance difference. You just ride it harder with a loud can on.