Help with Tri-Vista Phono Section.

I just recently purchased a Tri-Vista 300 Integrated Amplifier and am experiencing what sounds like a 60 cycle hum while no music is playing between songs of an LP. My turntable doesnèt have a ground to connect to the Tri-Vista. My turntable has a MM cartridge. Does the phono section have an internal switch that enables you to select either MM or MC cartridges.

Any advice would be greatly appreciated.