[LiquidDan]

Hi, I am using a AKG k712 pro from a project ember amp.
It worked great for a year, now I am hearing a high pitched interference/background noise and I cannot figure out how to fix it.
It is not a source issue as I can unplug the input cables and still hear the sound.

Moving my hand near the amps power input makes the sound go away, making me think it is a magnetic/electric field issue with the power cable.
Any ideas on how to fix this issue?

 

[JustinBieber]

My first guess would just be a noisy tube. Try replacing it. It could also be a ground loop issue but usually that is a lower pitched hum not a high pitched one.
 
If you need a replacement tube I can mail you some for free. I have a lot of 6DJ8, 12AU7, etc ones lying around not getting any use