This has me puzzled.
I have this project:
Rendered with these settings:
In Reaper, through my monitors, it sounds pretty damn good. I'm working out mixes for drums/bass, and I'm happy with the direction it's heading. So I'm mixing it down to play on my computer speakers and in my car to make adjustments.
Note: I've done this all along, and this is the first time I've had this problem, so the issue isn't that my PC speakers are going to sound different than my monitors. This is something else.
When I mix down to .wav, it sounds like utter ass. The rhythm tracks have all sorts of phasing going on, and there's Reverb coming all over it from.. Somewhere.
What the fuck did I do?
Restarting Reaper fixed it.