How do I stop the Humming from my LP12?

Hi all this is my first turntable. I am new at this. I have two problems. I purchased a used Linn LP12 circa 1974 with the original power supply, Infinity Black Widow tonearm, AT - 30 Moving coil Cart, AT step-up transformer, Creek 5350 Integrated with built in MM phono amp, Vandersteen 2ce speakers. The cartridge came premounted by Brooklyn Audio. When I play a record, the music sounds good, but when there is no record playing there is an audible hum coming from the speakers that gets louder as increase the volume level. When the Amp is in any other mode like CD or Aux, there is no humming noise. Any thoughts as to what this is and how to eliminate it? My second problem is that with the table set up according the instructions I can hear the belt rubbing against the top of the guide that it threads through when it is spinning. Even when I try to adjust the belt to the bottom of the subplatter disc, and then replace the platter, the rubbing continues. Any suggestions would be appreciated. Thanks - Dave