This is likely a general belt drive question, but the Blvd S40 is quirky bike.
The wife's S40 started making this ungodly noise one day. I didn't ride it much, so I didn't recognize the sound right away. Then it hit me. Sounds like a slipping fanbelt, but a trill rather than a steady whine.
Sure enough, the rear wheel adjustments were off a bit, and the left side of the belt was showing some tooth wear.
Evened up the rear wheel, and it was less loud, then one day it just stopped!

Me: "Hey babe... I fixed your bike!"

Her: "My hero!"

She goes for a ride, loves the bike again. We stop somewhere, leave...
Her:"IT'S DOING IT AGAIN!"

Me:"Uh..."

So now it does it on and off. Some days it is silent. Some days it chirps. One time, she bounced the back wheel against a curb a few times and it stopped... Which I would think would happen with the adjusting bolts set... I can't see it slipping backwards?
Any thoughts. Any S40 owners having similar problems?
Thanks,
Dave