Recently the navi voice guidance and beeping for skipping tracks are not working. What can be the problem?

And it's not the hardware volume level. It is pauses with no sound when navi guidance should be saying something.

Anybody have an idea? Which wires are for the system voice and beep and are they seperate from the wires leading to the speakers? It's been awhile since I installed mine.

I had this happen on my N1, I had to pull the power wires and plug them back in and it started working fine again. I'd like to get to the bottom of it as well, it hasn't happened in over a hear now though.