Whenever you navigate into a folder or click back or forward buttons in Windows Explorer, it plays short "click" sound. I imagine there's a way to turn that off, but haven't been able to find it.
"It's like a clickin' noise!"
You can disable all Windows sounds by going to Control Panel > Sounds and Audio Devices > Sounds and using the drop-down, choose No Sounds. For just Explorer based programs, scroll down to Windows Explorer and find Start Navigation and click that. Then choose (none).