annoys me. They see caravans being pulled or trailers with a bit of cardboard for a plate yet they'll pull the motorcyclist for the slightly too small plate.
They see chavmobiles with horrendous bean tin exhausts that are modified to the point where they're unsafe but they'll pull the well maintained motorcycle with an grand worth of Akrapovic that's slightly too loud. As I say, there's antisocial exhausts and there are slightly loud exhausts. I don't endorse the former but the latter are perfectly fine by me. I can think of two occasions in the last couple of weeks where a louder exhaust could have made my life a lot safer and saved me jamming on the brakes.
I think so many offences are overlooked for petty offences committed by bikes. I don't see the point in small plates but still, they do nothing about someone sticking a bit of cardboard with felt tip on it. You can't have one rule for one and one for the other.
If I were a copper and I found someone with an exhaust that was slightly loud I'd absolutely ignore it. If it was antisocial and making me vibrate then yeh - I'd do something about it. Also, I'd only use a slightly small plate as an excuse to pull if I needed one but frankly again, if you take the piss you're asking for trouble - if it's not even close to legal or a US style plate or you've put a black screw head in there to make it say something else then yeh. That said, do they clamp down on show plates on cars where the font is slightly wrong or they're misrepresented in order to spell something? Of course not judging by the number I see.
Keep it legal and you won't have issues - don't give them a reason to pull you and start potentially picking up things you've not noticed. They tend not to give advice any more but they're obsessed with targets which stops people thinking. Check boxes in public service may improve stats but that's because they're aiming to improve the stats. In certain cases it works, but in other cases it fucks things up.
EDIT: As for "inherently loud" - I agree - UTTER SHITE! Yes it's probably technically more difficult to quiet them down as the exhaust is shorter but it can be done and some bikes are almost dangerously quiet. Such as mine.