So now that Ventidue is all paid off, the strange sounds are starting.
There is a (what a would call) a belt squeak when the engine is cold, and tends to go away after about 10 minutes of run time. It definitely gets louder with increased RPMs.
The belt seems to be in good condition. Scott and I put a new one on about a year ago while installing the Alta pulley (right before he went to start up Det Monterey).
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Update #1
The squeaking is not getting any better.

I was looking at NAM and someone mentioned that the belt tensioner might be out of limits - you are supposed to be able to see holes aft of the spring. I checked mine out and I don't see the holes back there, only about 1/4" until the T-stop. Can someone with an Alta 15% pulley go take a look at theirs please?
I will try to take pictures tonight when it is dark. I couldn't get them to come out in the sunlight.