Sorry I missed your repost. I covered most of the common reasons for the buzzing. It appears that your alternator and regulator are OK and the wiring harness is fairly new.
This leaves a wiring issue or a possible short to ground in the charging circuit that is not fused.This short may be throwing the alternator into a full charge output mode and if the short is intermittent it will cause the alternator to cycle between normal and full charge.
Another possibility is that the blue and white wires from the regulator are not making a good connection on the alternator end or the regulator end. I would do a continuity check on those wires and also check for a full 12 volts on the red wire at the regulator plug. This is the sensor wire which tells the regulator what the system voltage is and lets it adjust the alternator output to compensate.
Check the voltage of the brown wire with the key on and with it off. 12 volts on and zero with it off.
Do you get a charging light or a flickering needle on the ammeter if you have a gauge dash?
A bad diode in the alternator could cause the regulator to buzz, If you disconnect the alternator plug does the buzzing quit? A shorted diode would be the short to ground I mentioned above.
A wells vr 715 is totally different to the points style and it is around $20 bucks. If everything checks out. It might be a solution.
Other part numbers for the solid state regulator are AC Delco # D663
and GM # 1119519. The sold state regulators shunt the excess voltage from the alternator to ground much like a Zener diode.
I know you want to stay with the OEM stuff but you wold be much happier with an internally regulated alternator.
Mid eighties 12 SI is the ticket.
conversion wiring is very easy.
Or you can even go to the newer CS style.
the conversion is just as easy but you need to wire in a 75 to 300 ohm resistor.
The brown wire goes to the L terminal and the red wire goes to the S terminal.