Default [Q] Audio characteristics changed; can't revert

Hi folks. I have a 16GB US GSM Moto G, and yesterday, the character of my device's external speaker changed.

Formerly, to get a good average sound level in apps, the volume needed to be near the high end, I'd say about 60-80% of max. Now, that same volume level corresponds to about 20-40% on the slider. At the same time, I started to get weird sound artefacts in one app (Tiny Death Star). I hear a light popping sound in the speaker about once per second, and every couple of seconds the sound stutters. Not terrible, but enough to be distracting. It doesn't affect all apps, but I haven't tested extensively to see if it's the only app affected.

There are a couple of variables:

1. Yesterday I installed the KitKat OTA update. I'm about 80% sure that the issue didn't start immediately after that, but I can't be positive.

2. I played with a couple of music player apps: WinAmp and PowerAmp. In the latter, I did mess around with some EQ/volume/balance settings, but I left everything where I found it. Once I noticed the new issue, I uninstalled both and rebooted the device, but the problem persists.

I also noticed the "Audio Effects" setting in the Sound settings. Tried turning that off, but it didn't change anything. I also tried wiping the cache partition; no change.

Anyone have any idea what may have caused this (and more importantly, how to fix it)? I could live with the volume range change, but not so much the stutter/pop.