You've saved Skyrim from Alduin the World-Eater at last. Surrounded by the souls of Sovngarde's mightiest heroes, you watch his bones burn bright as the dawn, then fall away to ash. What sound accompanies this event? "Blink blink blonk!" Steam would like you to know you've just unlocked the Dragonslayer achievement, which it does by loudly playing a cheerily rinky-dink sound effect.
While Steam's Big Picture Mode has had an achievement notification sound for a minute, as Steam Deck owners know full well, Desktop Mode remained classily silent when that little rectangle appeared in the corner of your screen. Now it makes a noise for every achievement, and when a game finishes downloading, and I hate it.
Fortunately, you can turn the noise off. As of an update earlier this month, Valve has "Added a toggle in notification settings to turn on/off sounds for non-critical notifications." All you have to do is go to Steam > Settings > Notifications and then hit that "Play a sound when a notification toast is displayed" toggle. Learning these notifications are called "toasts" has only made me hate them more, by the way.