Perhaps the gunfire you heard was perfectly legal fire, coming from private property?

Seems to me that the expectation of "non-offensive noise" is not enforceable.....otherwise I'd have ticketed those commercial airline pilots who fly over my camp daily.

FWIW....gunfire in the woods is pretty common in MN and often legal.  You want action....you gotta call the sheriff....then you need to convince them why they should come out to investigate.  Hearing gunfire alone (no matter how offensive to you), is no reason to investigate....IMO.