(reprinted from HowToGeek.com)

The Windows Explorer click sounds are enough to drive you crazy after a while. You’d think that the configuration option to turn them off would be a checkbox saying “Stop Annoying Me”, but that’s just not the case.

To open up the sounds configuration panel quickly, just type in mmsys.cpl into the start menu search box, and hit enter. You could also go to the Sounds and Audio devices in Control Panel, or even type Sound into the search box.

Click the Sounds tab and then browse down in the list to “Start Navigation”

You’ll see that the dropdown box has “Windows Navigation Start.wav” selected. Change this to (None) at the top of the list.

Hit OK and your annoyance is over with.