When I got my mota, there was (and still is) a Peco DTM on it which gives a nice deep burbly sound which i quite like but late at night when I`m comin` in it`s a bit too loud plus there`s the drone that you get when cruising on the M`way.
What I wanna know is will a replacement standard back box restrict/impede the engine in any way if I were to fit one.
Yes, the standard one will restrict your exhaust . You'll lose some power at the top end but it may feel at bit more torquey at low revs. If your going to get a replacement make sure it's the straight through type (though may be just as noisy) or buy one from a good quality manufacturer like magnex (i think they dyno test theirs).