The link V-belt material I had must have been defective because it made
a constant buzzing sound.  Urethane belts need to be properly tensioned
and there is some trial and error to it because they initially stretch.
They are so sticky that they can ride off the pulley, especially if you
are using a round belt.  It is best to not use the round belts for high
speed operation.  It also helps to lubricate the belt with a very light
wipe of mineral oil, as recommended by the manufacturer.

I was getting really quiet belts from the local (not NAPA) auto parts
store a bunch of years ago and then they changed their manufacturing
procedure and they got really noisy.  Then NAPA Auto Parts started
having good ones but I have not bought any recently.  It's probably
a good idea to buy some spares when you find good ones since the next
batch from China might be totally different.

Best regards,
Spencer Chase
Garberville, California
http://www.spencerserolls.com/