i had the same issue, I love the way to GTM sounded, make sure you buy the most recent version. I had one mated there x pipe and it made the ringing noise. Also the gt2 is very nice and loud!
BMW E92 M3
EVOLVE Stage II | EVOLVE X-Pipe | EVOLVE E-Tronic Exhaust
Macht Schnell Stage II intake | KW V3 | Volk TE37SL | BMW Performance Spoiler
Apex Stud Kit