Gizmodo has a great piece about obsolete tech sounds - sounds we used to hear all the time but have now virtually disappeared from our world.
Here's my favorite description:
Dot Matrix Printout
Long before the days of color laser printers that churn out 30 pages a minute, we had dot matrix printing. There was something hypnotically relaxing about the sound of the chirpy print head moving from left to right as reams of paper slowly pulled past it. We could meditate to that sound."