I asked here last summer about intermittent static and chirping from the
engine alarm buzzer. Lots of theories, loose belts, flakey wiring, etc.
The problem came and went and then cleared up.

I asked the local boatyards for the alternator "go to guy" in the area and
took it in. Before both my feet were across the threashold he said, "Oh, a
Yanmar!"

I told him I was bringing it in for checking and about the static from the
alarm speaker. He said, "You've got bearing issues." I handed him the
alternator and he wiggled it so I could hear the faint click, click and
said, "Yup. Rear bearing."

The bearing wears and allows enough movement for the rotor to hit the
stator. It first hits very lightly on the closest part making the chirping
and static. The high spot sometimes gets knocked off and the the sound
stops. The bearing wears some more and it starts again. Eventually, the
contact becomes enough to stop the charging system. By that time, the
stator or rotor are usually worn enough that the unit has become a
paperweight. Since mine was still charging fine, it may be repairable.
I'll know in a couiple of days.

I asked if I should undertake the very difficult job (on my boat at least)
of renewing all the wiring and he said, no, this was definitely the cause of
the noise I was hearing.

--
Roger Long