You're probably following this tutorial: https://developer.valvesoftware.com/wiki/SteamVR/Environments/Adding_Sound/Soundevents

Here's a couple things I had trouble with that aren't in it:

-The sounds directory isn't in your addon's directory structure by default; You have to add it.

-Sounds will not play in the asset browser if the headset is in standby mode, so if it's just sitting on your desk and the vr window is black you can't verify that your sound works.

-The .vsndevts file does not properly compile until the engine loads up for some reason. So if you've done everything right and are still not seeing the sound asset appearing in hammer try building and loading the map.

Hope this prevents hours of frustration for someone.