Did you go to Powerflow "proper" in Milton Keynes or somewhere else? Mine's going to need some work on the 'zhaust at some point, but before then I'll need some additioal protection for the underside. Mine's standard apart from the slightly modified Trooper rear section (£12 I think - I have a spare one thanks to the unique way Millner's dispatching works...) which got re-shaped to fit by my handy local exhaust place.
Its a fair improvement over the embarrassing spud-gun that was on it before...
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edit:- meant to add that exhausts definitely change their tone as they carbon up to don't panic too much...