They sound pretty good. I've only heard Mototrbo "noise" as interference to analog, and never actually heard it demodulated. Certainly sounds better than 155.175 did. Unfortunately some people seem to mumble.
Is the sound at the beginning of some transmissions a channel grant, like in legacy trunked systems, or does it mean something else (or does it mean nothing)?
I might have spoken too soon. Sounds like there are some issues with some kind of feedback, like it's breaking into oscillation. What kind of receiver are you using?