Got a 1972 Buick Skylark Custom 350/ 350. Had an electric issue with the car which resulted in changing the alternator and regulator and battery. I think a bad earth to the alternator was the start of this but is now rectified. So, three regulators and three alternators later and a new battery she is now behaving herself. Well sort of, despite the alternator and voltage regulator doing their job, the generator idiot light will flash up and an audible buzzer noise can be heard. But there isn't a problem with the electronics. Why would this light and buzzer still come on. It's getting ridiculous.
Be sure the alternator plug is completely in and making good contact. Some times the wire will push itself out of the plug when you install it causing the Buzzing and light flashing . Voltage Regulator is on the firewall and when it "Buzzes " it sounds like its inside the car .
I've been buying AC Delco voltage regulator from Rockauto, I've bought three of these in two months. I borrowed a voltage regulator of a friend's car as I knew it ran great. Problems stopped immediately, I'm pretty I must be the only guy to get three duff voltage regulators in a row from Rockauto, they must have had a bad batch.
An electronic regulator would probably solve your problem. As to why it is happening, there are multiple possibilities. Does it happen under all conditions, like at all rpm, under load or no load, hot or cold?
I went with the cheap ugly electronic one after having bad luck with a couple of the old style . Once I verified it worked I swapped covers. Patrick
My Son and I went they this exact scenario couple years back, buying the expensive $78 “Made in USA” from several sources and all being the electro-mechanical type and could never get them to behave right..........Then bought the cheap $28 Chinese made electronic and haven’t looked back, also switched the covers so they look correct ......done!