This is on a Moto X with Android 4.2.2. Not rooted, no EQ installed or enabled.
I primarily listen to music through DSub (streaming audio from a Subsonic server), but I've talked to their devs, and they don't perform any volume changes of any kind. Likewise, the Subsonic server doesn't make any volume changes, and I haven't experienced this volume issue when streaming to other devices.
Every time a song starts, it plays very loud for a few seconds, then drops slightly to normal. If the song starts loud, it can be quite a jolt for a few seconds before it drops down. It's almost as if it starts at max volume, then drops to the volume level I have set, but I haven't tested that.
As far as I can tell, there are no Equalizers enabled. Turning off the "Audio Effects" settings panel doesn't seem to have any effect on music playback.
Any idea what would be causing music playback to start off at a different volume?