I don't really know the dB rating, but it's not *that* bad. More on the Panaflo side than Tornado. :/
If you already have a running and quite silent PC and have the fan at your disposal, you can try and plug it on the Chassis fan mobo connector. Or maybe with an 3/4 pins adaptor and a PSU w/ tester. Hope that helped.
i think dba would be around mid-high 20s, cfm won't be too high.
i think stock ones are quite, but if u want something better n quite go for zalman 7k series.