Hum prblems can be very frustrating, and there are no hard and fast rules because everything depends upon everything else, from the components in your system to the wiring in your house. That being said, you should try connecting the ground wire from the tonearm to the PREAMP, instead of the phono section. This will usually lead to a much quieter background. The phono section will be grounded to the preamp through the line level interconnects.
Good luck!
Good luck!