You mean is the officer from your city's PD gonna give you a hard time for your made-in-Idaho suppressor that you haven't registered or paid the $200 tax stamp for?
Under Idaho law, he can't. Under Federal law, I think he has no jurisdiction. but if he really, really didn't like you, I guess he could blow the whistle to the feds, who would probably love to fight you on it.
Technically, though, the federal law on that kind of stuff only affects INTERstate Title II weapons/accessories, and if it is made and stays in Idaho, it's an INTRAstate Title II weapon/accessory (which is why we get to have our "exemption from federal regulation" law.)