From the beginning, my powermatic 15hh surfaces has intermittently made this clattering noise. It’s on warranty so I’ve not worried too much but it bugged me. It was pretty weird because it seemed to stop the instant I turned the machine off so it would spin down silently.
I called PM about it and their tech support guy had no answer.
so I opened up the cabinet, lifted the motor and removed the belts. It took about two seconds to see that the motor fan impeller was very loose and was clattering against the shroud. Tighten a set screw and problem solved. My guess is that the impeller was loose at the factory.
So I called PM tech support and told them. I was assured that if another customer complained of “clattering” they would be directed to check the impeller.