Sounds like you have been given good information from your mechanic. My Mirage does exactly what he described. If it has been raining for an extended period or it is quite humid out, my Mirage will do a short screech at start up. I think nothing of it. It only happens after long sits during those conditions. The rest of the day it is fine.
A better serpentine belt may help eliminate this, but I surely wouldn't sweat it. I believe the NAPA belts are quality belts. I would't worry about it, or let Fummins yank your CVT chain. :)