Maine State Code: can't fire a weapon from a point or have a bullet come within 100 yards or 300 feet of a building without the permission of the owners of the building. Also, I believe, but do not know that the bullet can't cross a road. (This, err, makes sense even if it's not a law). In towns more populated than where I am, this might be pretty restrictive, but if you've got five miles behind you I suspect you may be able to swing it... (Please have a backstop and check for any atv or snowmobile trails and stuff back there, too)

Also, as others have said, some municipalities will have more restrictive laws. Where I live, they do not.

I'd call my town/municipality office and ask. I tried calling the county law enforcement folks where I am (my town doesn't have any) and they just quoted the 100 yard limit back to me ....

Culturally, let people know (assuming you don't want to be a bad neighbor) and don't be an asshole with the noise.... But generally, no one seems to care much. I shoot several days a week in my back yard and I hear shots from others on a pretty regular basis.