I've used Noisy for OS X and also Aire Freshener for Windows (which includes ambient recorded sounds such as rainfall) but notice that after an extended period I tend to have "aural hallucinations" -- I start hearing patterns in the noise that aren't there. This usually worries me and I have to turn it off.
It does not appear to be free.
It immediately started playing noise when I visited the site. How is that not free?
It didn't do that for me on Chrome, and it links to a "donate to download" page. Odd.
Chrome dev build for OSX 10.6.5 here. I find this odd. Any thoughts on why this might be?