That is an interetsing point. Being on private property and not even driving would make me call my lawyer on the spot. Though most people probably don't have a lawyer they can contact.
That has go to be the most blatant bit of revenue raising I have heard yet. The exhaust thing might be an easy fix as well, relatively. Just get another muffler put inline to keep it under the limit on back-off.
Go an read this and see if your wheels are indeed legal or not.