We seem to have quite a little community of 513-whatevers out there. As my saw was winding down a few days ago I noticed a kinda of clunk-clunk-clunk-clunk that followed the motor rotation, not the blade (I dress my welds).
I wrote Grizzly tech support and in their usual fashion, they were all over it. They had me pull the motor cover and found the fan/centrifugal unit was cockeyed. It is retained by a split-collar grip to the motor shaft for orientation and linear position. I adjusted it.
During the time I had waited for Griz to respond (overnight), I had done some troubleshooting on my own. This led me to remove the belt (noise still there of course as I hadn't found the real problem), removed the pulley, etc.
I figured as long as I had the belt off I would put on the link belt that I had hanging on a nail. Along with silencing the clutch noise which I always assumed was normal (till is got louder) and the addition of the link belt, I cannot believe how quiet and smooth this guy runs (nickle test no problem before this effort).
Here is a shot of the throat restricter I added (I've seen these on those cool Italian jobs at the shows) which has drastically helped in my dust collection. I sometimes just seal off the lower hose now as so little dust gets by this area. Hope this helps any others out there who want to tweak their machine.