.22 rifle shooting colibris is quieter than a spring piston air gun. Especially if you fire from 6 ft. inside your window. Or so I've heard.
Maybe, maybe not. My BSA Supersport 22 air rifle had more thump (wish I hadn't sold it). Sorry, I imagined a comment about power Also, you shouldn't shoot Colibris from a rifle. Maybe Super Colibris, but not the regular ones. Finally, if you were to fall afoul of the po po for shooting a gun on your property, you're more likely to successfully feign ignorance if it's an airgun.
I've never been a fan of Gamo because of how they inflate their velocity numbers using the lightest pellets possible, but they're supposed to be decent guns. That said, if I were going to buy an airgun today, I'd probably go for a Benjamin pump gun.
CO2 can be loud. I owned a Crosman 22cal similar to the K2300 Rooster linked to and it was shockingly loud.
Chris