2001 Hyundai Tiburon voltage fluctuation non-constant

Hello,

This is my first message on the board :)

I have a big issue with my car (Tiburon 2001). I drive for a bit (15-20 minutes) then al off a sudden the voltage start to fluctuate like the regulator on the alternator does not output 12v anymore, then I have voltage peaks and some of my front and tail lights burn off.

At first, I thought it was a short in my lights because after that I could continue driving. I went to a car electricity specialized garage, they could not reproduce the problem but they check the whole electric cable, alternator and fuses and they found nothing so they assume my alternator was the issue.

The alternator was just 6 months old because my original alternator (8 years old) died. So the alternator was warrantied and was changed.

Got back my car, drove shopping the next night, lights open, heat fan on radio on as usual then on the exit of the highway, the fluctuation start again, and I hear electric interference in my radio speakers (high pitch noise that goes higher with revving the engine more higher) so I decide to turn off the heat fan and the noise stop and the voltage goes back to normal. Luckily for me I did not burn my lights this time.

I wonder if it could be a short in the heating fan system? I am still not 100% sure it would not do it with the fan off but I think I should ride it a couple day with everything on except the fan maybe?