As the launch customer for the Grob 115 series in Canada {My wife and I owned a few flight schools, since sold to staff and customers, old age the only reason} I just cant belive that the RAF finds them to be too loud in the cockpit, we regulary flew eight hour aerobatic days, all are still passing our six monthly hearing tests,
Clunck, I was equally sceptical as my hearing has not changed in 9 years of flying the machines. But it's the frequency (80-100Hz) that's important as most hearing tests don't go that low: the RAF tests from 8kHz to 500Hz.
McD