Sound quality issue on new Z390 Opencore build (audio sample included). Any suggestions?

Hey everyone!

Got my first build up and running a few days ago, and while almost everything works perfectly, I am experiencing some odd sound quality issues. I'm currently listening to my audio through the 3.5mm jack on the front of my case. The sound quality sporadically jumps from being muffled to clear and is a bit staticky.

I've dug into a number of different scenarios that sound similar to mine, but I hoped that someone here might be able diagnose exactly what's going on.

Here's a sample of the issue: https://clyp.it/xyfxysf2

Any help is greatly appreciated.