thx for bringing more suggestions that may help me troubleshooting this issue. I'm not using USB, I mostly use RCA. Actually the USB cable wasn't even connected when I first noticed the issue. I have tried with USB and no difference. Actually, even without any sign sent to the dac or cable connected (appart from the audio out) I get the same issue. When I first turn it on, no issues at all, but after an hour, give or take, this hum starts.
By the way, one of the reasons I got this dac was also after reading some of your reviews and mods :) I actually waited for a few months to see if you were selling any moded orchid :) ... just a side note. Thx once again, I appreciate your message. I'm starting to think I can't escape to send the dac in for repair.