Alas, I could not find a low power, ultra-low-noise motor with air bearings, and I have not got around to replacing the sleeve bearings with air. It’s pretty fiddly!
But those sleeves are a problem. This is demonstrable by removing the belt and manually bringing the platter to speed. The latter sounds more refined, less high frequency hash. When the belt is restored, hash returns. When the motor is turned on, nothing changes. Hence it is the motor’s sleeve bearings to blame, not cogging or other electro-mechanical effects.
This is a little surprising, given the platter's mass, about 45 kg.
But those sleeves are a problem. This is demonstrable by removing the belt and manually bringing the platter to speed. The latter sounds more refined, less high frequency hash. When the belt is restored, hash returns. When the motor is turned on, nothing changes. Hence it is the motor’s sleeve bearings to blame, not cogging or other electro-mechanical effects.
This is a little surprising, given the platter's mass, about 45 kg.