Okay, this might be the answer to a question nobody asked, but I thought it was kind of cool. From the tech site Mashable:
Did you ever long for the romantic old days where the act of writing evoked the sound of clacking typewriters punctuated by the chime of a bell?
Then the Noisy Typer 1.0 is for you. Theo Watson, an inventor, introduced the free app earlier this month. It may be the perfect thing for the nostalgic and/or pretentious writer in your life, especially if she happens to be a Mac user. Unfortunately, no Windows version exists yet.
Check it out:
I will caution you that it would be very annoying to the people around you if you used this app while you're working in a coffee shop, so download it at your own risk.