Faint alarm sound when I turn the boat on

[Green Horn]

Today as I got ready to head down the ICW, I turned my engine on and it fired up just fine. But once it was in the "on" position I heard a faint alarm sound from the starboard locker. If I turn the engine to "Off" the engine still runs and the faint alarm stops. If I put it back to on then it resumes. The loud normal alarm sound still works fine.
I saw on the internet that this might be a voltage regulator issue. I have a Yanmar 3YM20 engine.
Also, when the boat is plugged into marina power it doesn't do this (there is no faint sound).
1. What do you think is causing this?
2. Is this a must fix here and now issue or can it wait?
Thanks so much for any advice you have.

[Frenchy]

Yes, you could have a alternator circuit problem. Check the battery voltage with the engine
idling-ignition "on"- should be somewhere around 14 volts. Good luck.

[Jim Walsh]

If I turn the engine to "Off" the engine still runs and the faint alarm stops. If I put it back to on then it resumes.

I was always taught to leave the key in the “on” position when the engine was running or you risked damaging the voltage regulator. The only safe method of shutting the engine down is stopping the fuel flow first, then turning off the key.

[Steve Laume]

I would be looking for the buzzer and any senders I could find. The idea is to find out what sets off this alarm. I have water temperature and oil pressure senders that go to one alarm. I also wired in toggle switch so I can turn it off when I start the engine. I hate the buzzer, mine is loud. The unusual one is what you are looking for. Once you find the buzzer and then the senders that set it off, you will know what you are dealing with.

Are there low voltage alarms?

I have always heard the same thing about turning off the key before shutting down a diesel. I think it depends on how your alternator is wired. If it always goes the the batteries there coudl never be a problem. I have turned off my key on Raven a few times before shutting down the engine. I also have a little Kabota backhoe that can only be shut down by turning off the key. With more modern diesels it seems as if you just turn off the key. Ours are more like a Fred Flintston arrangement where you have to pull on a long cable to strangle the engine to death.

Let us know when you find that peskey little buzzer, Steve.

[Green Horn]

Hi guys and thanks for the advice. Since the day it happened, it has not happened again. I'm going to check the sensors and power just to be safe. If I figure out what caused it I'll be sure to post it on here.
Ed