GCPH hum or buzz

I’ve recently purchased a preowned GCPH phono preamp. I like the unit, but my problem is I get a very annoying hum/buzz when the unit is turned up past 2 o’clock (2/3) volume. I’ve heard others have had this issue, but I have not heard a solution. Is there one? The hum is there whether or not the turntable is connected. And I’ve relocated the GCPH away from other units, and the hum isn’t affected, it’s still there. My other preamps never had this problem. Help?

Followup: To anyone else who has encountered this issue, I’ve found a solution on another forum. Open up the GCPH case, slightly loosen the nut holding the transformer in place, and rotate it slightly until you don’t hear any more hum when the unit is hooked into your stereo system (take care not to touch anything else in the case if you don’t know what you’re touching!!! – beware live electricity!!). Apparently the transformer can create hum in the circuit if it is facing the wrong way. It works like a charm.