Classic 3 VPI

You have probably transferred some "natural oils" during handling and now they have coated all surfaces.

Powdering the belt is a temporary fix and does not address the real issue - belt slippage - you need more grip - the powder allows the belt to slip silently until the platter is spinning - result, no squeals, but the powder wears off and makes a mess on the plinth

You might want to consider cleaning the belt and all surfaces that come into contact with the belt thoroughly (I've used isopropyl alchohol) it will give the belt more grip and hopefully eliminate the squeel.

I've had this issue for years on my "Rega" and cleaning has yielded the best results, but  if that does not work, you will have to resort to the "Rega nudge" on startup - you just give it a little push and then turn the power on.

If you change speed a lot I would recommend getting a pair of cotton cloves when handling the belt.

I do agree with other posters about running multiple belts - that is a big platter to get moving and one skinny little belt probably will not provide enough grip.

Regards - Steve

My Prime gives a small squeak upon start up with no assistance.
I've gotten into the habit of giving the platter a little help when pushing the start button, and there is no noise now.
Just a slight clockwise push on the platter while engaging the motor.

I know of other turntables that require this to get their heavy platters moving.

Yes, clean the belt, but remember you also need to clean the perimeter of the platter.  Isopropyl alcohol is fine, or ROR (residual oil remover) if you're so inclined. Also, wash your hands thoroughly before you begin the operation.  

Spin the platter by hand before you push the power button. Both of my VPI TT's do the exact same thing.

+1 for spinning by hand!