Funnily enough I have had some hum issues with both the Analog Four and the Analog Rytm.

I thought I might have a ground loop issue but it turns out I have a problem with my headphones, my Urbanears Zinkens (came free with an OP-1) have a hum but my Audio Technica ATH M30’s and ATH M50’s both give a clean signal.

I figure the lead on the Zinkens has gone stereophonic (if that’s the word).

I’d suggest trying a different set of headphones if you can.