If you have sox (free, cross platform, open source) installed, you can run e.g.: play -n synth 08:00:00 pinknoise for 8 hours of noise -- you might pr

If you have sox (free, cross platform, open source) installed, you can run e.g.: play -n synth 08:00:00 pinknoise for 8 hours of noise -- you might prefer either whitenoise or brownnoise, and maybe play around with the eq or other effect options to modulate the output if you want a little variation. If you skip the duration it'll play til you ^C.