Hum is typically a ground loop or lack of ground... and could possibly be a bad RCA or ???...
I would first check all cables... make sure they are fully inserted to the receptacle. This includes 120v, RCA, etc. AND... the ground from the TT to the phono preamp (or preamp, if phono is built in) Also, check the tiny wires from tonearm.
If hum is still present... change RCA cables one at a time. You may have a bad solder joint or broken ground conductor.
As a last resort.. (in my opinion) you can try ungrounded 120v cables on grounded equipment.