I don't know if this is at all useful in recommending a solution for me, but if I'm touching metal from my amp or DAC and also touch the metal connectors on the RCA cables the hum goes away completely. Edit: Found a temporary solution. Still looking for a more permanent one. Using a 2 prong power cable with the Kenzie Encore eliminates the hum. Initially I tried the 2 prong power cable with the Metrum Onyx, and it did not fix the issue.