ejlif, I have/had the same issue with the Decware, it is the tube.I swapped the tube to my preamp and the ringing was now at the preamp. Tube rings may help, If I hold the tube the ringing stops.Also seems to come and go while using amp. Yes this tube is an
Elecrtro Harmonix 5u4. So Try another tube, hope this helps you.
Elecrtro Harmonix 5u4. So Try another tube, hope this helps you.