Try making sure libao is using esd?
Check /etc/libao.conf:
I assume you've already made sure mpd.conf has audio_output with type ao, as above...

I'm on an N800, but sometimes such troubles befell when I was fiddling with it. (I still don't really understand the sound system, and especially how it switches between BT and internal DAC.) Oddly, alsa seemed to work fine with BT earphones, but broke up with analog (either speakers or headphone jack).