[Bryan A.]

It's from the air in the mixture. You could try mixing slower although I have found that doesn't help much. Or use a high build primer after the fairing is complete. I'm sure others will chime in with recomendations.
You could also use a premade fairing compound. I have seen others use Quik Fair by System three, it is packed under a vacuum so no bubbles, but I have not used it myself so I do not have first hand experience.

Hope that helps, Good Luck. Pin holes suck.