The quietest "compressor" you can get would be a bottle of dry nitrogen. It is sold at any welding supply place. The bottle comes with a pressure of @2500 psi. As you use the nitrogen, the pressure drops, when you get down below 10 psi, you take it back for a refill. The initial cost is a bit pricey because you will need the bottle, and a cart to tie it down as well as a pressure regulator to drop the pressure from the 2500# bottle pressure to your 15-30# working pressure, but the gas itself is cheap, so refills are not bad at all. If you use dry nitrogen for spraying, you won't need a water separator in line to keep moisture out of your paint. Nitrogen is an inert gas (72% of our atmosphere is nitrogen) so it only has one safety drawback. Nitrogen in an enclosed space will displace oxygen so that you can't breathe in such spaces, but the amount of nitrogen in a small bottle will probably not be an issue in any space you are spray painting in.
If you want to get a compressor, check out your local Home Depot, Lowes, etc. They sell small compressors for contractors to use on job sites. You want to get a compressor with a storage tank that will give you a steady flow of air. The little hobby compressors have no storage tank so you get a pulsing air delivery instead of steady pressure. You will also need a pressure regulator with a water separator. I think any compressor you get will be noisy, but you can reduce the noise if you build an enclosure box big enough to fit over the compressor. I would suggest cutting a hole big enough for an air intake and filling it with foam or some furnace filter material to preclean the air going to the comppressor. If you line the box with some foam or cork to muffle the sound that should help as well.
