If you are using a tube power amp, there may be hum originating from the amp or the tubes. Also, as mentioned above, definitely check the polarity of each component, and interconnects. Cable quality and placement are also important. There may be a ground loop. I was able to get rid of one source of hum with using a battery phono preamp. Good luck!
Low level Hum in Phono Signal Path
There is a distinct low level hum noise evident through my speakers when the phono mode is on. Can't be heard from the seating area but can be heard when your ear is in front of the speaker, either side. This noise is also dependent on the volume; the higher the volume the louder the noise. What is causing this noise and can it be remedied. (Equipment involved: BAT PK 5 phono preamp, Transrotor turntable with Benz Micro Ruby 3H cartridge)