Hum in tube amps.

Being fairly new to tube amps.I would apriciate any help. After a few months of listing to my gear.I now here a buzz comming out of the speakers.The unit was dead quiet up to now.Can anyone give me a sequnce for troubleshooting this.Where do i start.The amps have 4 KT-88 2 12AU7 1 12AX7 per side.The pre amphas 2 12AU7 line Stage 4 6922 Phonostage.The only change i have made was adding a Turntable.I have disconnected it suspecting it was the source but its still makes the buzzing sound.Thanks in advance.