You may consider a .410 Bore shotgun if you're concerned about noise, Mick. It's MUCH quieter than a 12 guage, especially with a longer barrel, and I'm sure it has the knockdown power you'd need for 'Yotes. They even have a few really nice semi-auto platforms out now. I've been eyeballing the .410 Bore AK shotguns myself recently, although a Saiga 12 guage suits me much better.

I'm no expert, but in my area, as long as you are outside of city limits, on private property with permission, or public land, and are not firing in the direction of other houses/have an adequate backstop, you're allowed to fire any caliber. The rules change a bit with huge calibers that can reach out and touch someone, same rules apply, but as a shooter I'd still be responsible if my .50 BMG (hypothetically <img src="/ubbthreads/images/graemlins/frown.gif" alt="" />) went through the wall of my nieghbors house 2 miles away. I didn't think sound was a concern unless you're within a quarter mile of another home, during daylight hours.

If you're firing after people are asleep, you may seriously consider a supressor for an existing weapon in your collection, if your state will allow you to posess one. The prices are actually fairly reasonable nowadays, less than 1000$ for most that I've seen, plus the tax stamp. They've got cans for .22s that are as cheap as 180$ apiece that offer great performance. It's a lot of paperwork though, unfortunately.