[SOLVED] What is this sound?

maybe try a clean boot - read instructions carefully and make sure NOT to disable any microsoft services or windows may not start right - https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows

since its random, run clean for a while and see if it still happens. If it doesn't, slowly re add programs to startup and start the services you disabled, If it keeps happening, its unlikely to be a start up program which makes it even more fun to figure out. Would need to look through the options of programs you run,
 
Sounds like a message notification noise from one of your numerous chat/communication apps. Mind sharing a list o all the apps that are running in the background when you hear that noise?
I FLIPPING FOUND WHERE IT'S COMING FROM! but i dont know how to make it stop... after looking in the Volume Mixer and waiting like a hunter, i saw the audio pop up from the "Steam Client WebHelper" and i'm still not sure what sets it off. Anyone know?
 
Solution