Since no one has replied to this, I'll take a whack at it and say something. You may even have had this solved by now. Who knows!
It almost sounds to me like there is something physically wrong with the unit or a very critical issue with the software.
Can you tell if the "clicking noise" sounds like it is coming from the internal speaker or if it sounds like something else within the unit? I know most of those units don't have much for moving parts, but I recall a time where I had a unit (Trimble Juno SB) that seemed to randomly shut off and turn back on it's own will. On some of those units I was reported having issues on, there were some that talked about noises, and some that don't. I do not recall what the noises sounded like though. Anyway, It turned out that the SB series was built pretty poorly and I discovered the problem was that the battery connectors didn't stick out very far and were easily bendable. So from repeated jostling, the battery had moved around enough and had folded the connectors just in far enough that it wouldn't keep the connection all the time. I don't know if the noise was from the battery jostling or due to something from it just suddenly losing connection, but what I ended up having to do was take a screw driver and re-bend out the connectors so that they would stay firmly pressed against the battery (I think I may have even needed to take a part the units to do it correctly). Once I did that, everything started working just fine. Completely random, but you never know, it is possible you could be having a similar type issue.
If it was me, my next step would be to re-install the firmware. Not a factory rese type ordeal, but full re-install of the latest firmware. That would eliminate the possibility of it being a software issues altogether. If at that point it is still not working, I'm guessing there is a physical defect and you are going to have to retire, do your own surgery or have the unit repaired.
Hope you get things figured out. Good Luck!
