Edit: My last subject line got me nowhere so I changed it. Maybe now someone will have pity on me and look at this for me. Otherwise, I will have to think of somewhere else to ask my question.

I have this odd line in the spectral graphs of some audio I have been recording. This odd "line" just below 16k on recordings made in a couple situations. If I go Turntable -> Receiver -> AD20 -> Nomad JB3 I get it. If I go Digital Cable -> AD20 -> JB3 I get it. If I go Digital Cable -> Audio Out from Cable box -> Line In on JB3 I get it. They only time I don't have it is when I go Mics -> Battery Box -> AD20 -> JB3 or Mics -> Battery Box -> JB3. Is this just an electrical thing where I am picking up the current flowing from the stuff plugged into the wall? (receiver, cable box). I can't hear any problems, but I want to know what the hell it is. I KNOW someone here knows the answer or can point me in the right direction.

Here is my spectral graph:
http://home.comcast.net/~rsimms3/spectral.bmp