Quiet is great. But, sometimes you need an auditory reminder on your computer. For me sharp noises cause discomfort. The tone of an alert or the repetitiveness of it can be distracting if not downright painful.
Back in 2012, I found some subtle alert tones. I went to share it with some of my fellow neurodivergent colleagues and realized, alas!, you could no longer find them cached on Lifehacker. Credit goes to Adam Dachis.
You can download them at this link ( mirror ).