I agree with Toby that there are better ways of handling Thayer Street's purported parking-noise issues than to clamp down on motorcyclists. Not to totally dismiss the concern of those driving this, but this also seems to smack a bit of the nanny state increasingly coming to small town Providence. Could you imagine a city like San Francisco trying to do such a thing?
Yes, the bikers might be somewhat loud, but they're also an easy target. Hunter S. Thompson's Hell's Angels remains the classic account of how small town mores can be used to make motorcyclists seem much worse than they are.