Hum and Hiss with Tube pre-amp

I recently got a McCormack DNA1 Deluxe and initially used the pre-amp section of my Arcam Alpha 9, and then a Creek OBH 12. No problems, but no excitement!!! I decided to try a tube pre-amp. I have tried a Melos MA 111 and a Cary Ae3 kit that was up-graded in many ways by it builder. Both of these units are reportd to work fine by their owners. When I put them into my system (front end of CAL DX 1 cd and Rotel -entry level- tuner) I get very audible hum (60 cycle) and hiss(like FM hiss). I have tried cheater plugs on both amp and pre-amp to no avail. It was suggested that I disconnect the inputs to the amp and turn it on to check for noise- I did this and there was no noise. This suggests the problem is elsewhere. Since the tube pre-amps worked fine in other systems, they do not seem to be the culprit. But then again, with the ss pre-amps there was no problem, apparently ruling out the front end. But that leaves NOTHING causing the obvious problem!!! Any ideas?? Thanks for any and all help. Rich