Stopping the turntable - You mean physically stopping the platter? Are you saying that even if power is applied, once you stop the platter the hum stops? Or does it happen when you shut off? In other words, is this hum maybe related to the drive motor?In any case, I'm thinking it might be a good idea to clean the mechanical connections, such as the wires to the cartridge and any other removable fittings or crimp connections.