Faulty Voltage Regulator? Options

[Rob-O]

About a month or so ago I replaced my alternator. The old alternator was a GM one wire unit with an internal VR that was attached using a modified mount. I think the heat killed it. When in installed the new (rebuilt) alternator I used a new alternator wiring harness and also installed an NOS voltage regulator onto the relay board. When I fired the car back up after install everything worked as advertised. In the last few days though I’ve noticed that when I first start the car that sometimes the voltage fluctuates. I thought it may have just been the gauge in the center console so I broke out the DVM. Readings showed that sometimes when I start the vehicle the volts hover steadily around 13.8v. Other times the voltage fluctuates from just above 12.0v to just over 15.0v. When the voltage spikes high I hear noise coming from the engine bay. I know it’s not but it sounds like a bearing running without lubricant. When the voltage drops to normal levels the noise goes away. Voltage spikes and noise comes back. I don’t have an extra VR handy but does this sound like a faulty VR? It is an NOS unit so not a newer style solid state.

[Lockwodo]

Make sure the alternator drive belt is in good condition and properly tightened.