Three things come to mind when I read this, two are pretty obvious to a belt-drive person, the other is something I have only experienced twice and both since joining AW in 2008.
The first is indeed a bad belt. I have never heard them make really loud squeals though. Usually they are more of a muted slipping. They don't scream like an old automotive fan belt or something because they aren't moving fast enough.
The second would be the spin cam bar being tight. Lube this with white lithium or Rykon grease - it should become easier to slide. If this is tight, it would also put more of a drag on the belt and cause option 1 more readily too.
Finally, the third possibility is something I've had happen twice recently and it's something I've never heard before. It seems that when these machines sit for some time or just age, they slowly loose their "lifetime lubrication" in the bearings. It seeps past the seal below the bearing itself, and the bearing over time becomes dry. When both bearings are dry, this can be a real problem. On a tight, lightly worn bearing, there develops this unholy screetch when polished spin tubes rub against the bearing at 500+ RPM. I first heard this only briefly at the start of spin, and it would be worse on a heavy load vs. a light one. One case was so loud I heard it from the garage into the house with the door closed, and my garage is insulated! The problem worsens as the oil seeps away.
My solution is a pain in the a$$, but you have to pull the machine apart far enough to add turbine oil to the centerpost - so all the way apart. It's a magic cure though!!!
I would start with the belt, or better yet, record the sound on a video and let us listen to it!!
Gordon
