That's bad. I experienced exacty the same 'drone' with the AC-Schnitzer exhaust. A drone at appr. 2300 revs 6th gear (70 mph) or 110/120 Kph. The drone was really annoying. I removed that exhaust asap, and put on the OEM exhaust back on. Problem solved. No drone anymore. With the 1M///, the problem can't be fixed that easy
As for performance? No difference at all between the exhausts: still 382bhp and 565 Nm (all cranck numbers).