Navman 3100 wind indicator erratic at < 10knts

At low wind speeds, my Navman 3100 wind display is erratic. It reads
true for a few minutes, then for a few minutes it reads garbage. It
tends to cycle between these two modes. At above ~10kts apparent, it
seems to work fine all the time.

The masthead wand (anemometer) and instrument are new replacements.
The only thing that I haven't replaced is the mast wiring, which is
new as of 2005.

What would cause such odd behavior? What is the protocol between the
masthead and the instrument? Is it NavBus? What are the electrical
properties? Is this an analog circuit? Could there be some sort of
grounding issue? If there is an intermittent connection on the wire,
why would it phase in and out while at the dock and not moving, but
then be fine and steady underway?

Any suggestions or ideas would be appreciated.

-JK