corrupted system audio

Sometimes when my Mac makes a sound (like when I drag a file into a folder or I empty the trash) it blasts me with this horrible staticky noise instead of making the sound it's supposed to make. It's very unsettling, and it happens about a third of the time the system makes sound. How do I fix this?

I should mention that I'm using an external usb audio interface, but I'm fairly certain that I remember getting these awful noises from my computer's built in audio interface as well.