Ok, just installed a patched v300, and flite...

My first observation is that both volume changes are incorrect - they appear to be to fixed volume values, and not dependant on previous volume setting.

But it also appears that volume control is being done twice - possibly once by sample scaling?? Try turning the volume right down with music playing and then try ttsd - you'll get 2 spikes, one of either side of the tts output. I'm going to take a look at pcmplay.c, as I have a suspicion that this may be happening outside of the kernel - and that with the overlay patch that volume changes may not even be needed.