I have the same issue on my SAN. The basic problem is that the alternator puts out very little current when the engine is at idle so if you are using a lot the voltage will drop.
If the buzzer is going to do you any good at all it needs to indicate the low voltage before it gets so low that you will be stranded.
In my situation the only time I have an issue is when I am running a lot of stuff: The stereo is going, three ballast pumps working away, maybe I left the blower on, and even worse if it is cold and I am running the heater.
At least my alarm just gives a short beep every ten seconds or so, easily ignored.
I recommend using a digital volt meter to see what the alarm is complaining about. If the voltage is 13 volts or more then I would adjust/repair the alarm. If the voltage really is low and there is a reason for the voltage to be low then I would just accept the fact that the alarm is doing what it is supposed to.