Hey
When playing certain types of music bass ( something with a higher toned fast hit bass ex, dance music) my voltage will spike very high like 15.5-16.2Volts and get flashing in my gauges,, But on something heavy and consistant like 3-6 mafia it will be fine staying around 14.3V I have an optima Red top, Iraggi 160/100Amp Alternator, 1/0 Gauge wire run big three under the hood and out back to the amps, using a 200Amp Fuse on a JBL PB1200.1 and Fosgate 400.4 Also there is a capacitor 1Farad in the system.
It drives me nutz cause it will make my amps go into protection.
This only started happening over time say last 2 months maybe 3
And with car off my voltage will be 12.1-12.5 where as it used to be 12.8V
When just driving down the highway the voltage will sometimes be fine at 14.4 but on say a colder day just running the van it will be at 14.9 - 15.1 steady.
Whats wrong with my 1993 Caravan heheheh, I was thinkin regulator but its a new alternator with the regulator inside so

 

I would have your alt. checked out. Sounds like regulator is about to 'toast'. I know you said it's a new alt, but happens even to the new stuff.