When a friend purchased his TR6, it was loud, VERY LOUD, a previous owner had opened up the twin boxes and emptied them out, and welded them up again.
It had to come off, and a standard system was fitted ( in fact my standard system, need to get it back at some point) And he mentioned he had swapped it on a forum, and someone contacted him really keen to have the loud one, despite us telling him it was noisy.
Saw the guy a year or so later, and he had been forced to admit defeat and the exhaust had been changed again, I think pressure from his other half and neighbours had a lot to do with it.
anyway, GT6 are sensitive to loud exhausts as the resonate in the cabin.