Same here. The best solution I found involves lowering the audio quality, but there is still an insane amount of fps drop.
Another guy on the steam community thingy said you can improve FPS by going
control panel>hardware and sound>sound>playback>speakers/headphones that you use>properties>enhancements> and then checking the "disable all sound effects" box.
Doesn't improve it significantly but sometimes it improves the general performance.
And then yeah that's about all I could find related to this.