A quick question?

are you listening to a digital or analouge frontend? if the latter, some hummin' is commun'. if the former, keep checkin' on such things as the effects of halogon bulbs/dimmers, ac/coax(tv) crosstalk or other sources of rf and associated electronic junk (lots of threads on the application of filters on 'fridge plugs, etc.). if you still can't find your source, i'd advise retunin' your pianos or just try to join in, hummin' along, singin' a song. :) -cfb

If you have any products that make use of a non-polarized two prong plug, try reversing that and see what happens. It might not specifically be the C-J that is humming but a combination of equipment connected to it. Sean
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It is for me. I was told that if you can't hear it from your usual listening distance it is not a problem.

A little hum is normal on a lot of tube gear from my experience.

Did you try the cheater plug on the pre-amp? Also try a shielded interconnect.