Electrical Gremlins - Any Help Appreciated

[bonnyguy]

I am new here but have used this forum in the past for other issues with great success.

I have a 2000 Bonneville with an intermittent electrical issue.
Comes and goes, but is now here with a vengeance.

Here are the symptoms:
You know it's coming because the volt meter on the dash starts fluctuating back and forth by about 5 volts as you are driving. This happens and is a prelude to the problem. Within a few hours the car won't start up right away and then after a bit more time won't start at all - as the battery is now dead.
This time when I jumped started it it ran for a while, then all the lights on the dash started to flash at once and it died. All the while there is almost a slight "sighing" or quiet wooshing sound coming out from behind the instrument cluster. Not sure what is going on there, but that sound is only ever present when this problem presents itself.
Is this something as simple as a funky alternator just not charging the battery, and why would the voltage meter fluctuating always be the tell-tale sign of impending doom?
I have checked fuses, looked for corroded ground cables, etc. that have already been mentioned here.
Any insight would be much appreciated.

[MrJiggy716]

is it sending out any codes when linked up to a reader? I'd try that. Perhaps the battery is on its way out ?

[bobgto65]

or the voltage regulator in the alternator is on its way out. Also check the connector and wires going to the alternator for cracks or possible broken or about to break wire.