Bill, this a transformer hum and is harmless.
Either you get some DC voltage on the AC line or your transformer is mechanically loose.
If you want I can sent you instructions how to remove the transformer cover(whre you plug your mains in)and thighten up booth transformer.
You only need minor mechanically skills to do it,but you need instruction for it.
Send me a private email adress where I can send pictures

Robert


800v3/218/271/8k.2/5k5s smile /5kC/DSP3200/Reviver/
TT-ELP/Graham Slee Revelation/Trinnov Altitude 32/OPPO 205
__Ayon/HB/Shunyata/Miltzow -- power cables,
__Ayon/Jungson/Miltzow --analog, Miltzow-- digital,
__Vortex/WMA ,