Reddit user noticed a new Steam beta feature that allows you to receive an audible notification when you receive an award

Reddit user brokenwiener has reported that the new Steam beta version of the game has an option to enable sounds when receiving rewards in-game:

Apparently, Steam has an Achievement Sound in Beta right now, and Achievement Tracking.
by u/brokenwiener on Steam

If you wish, you can switch off the sound of notifications in the desktop client. However, there is currently no separate switch for achievements in the beta, so you can only mute all non-critical notifications at once.

It's not yet known when Valve will move this feature to the stable version of the launcher, or if it will do so at all.

Source: reddit