Humming when unplugging an output connected to BeePre

[Jameson]

I have the BeePre sending its unbalanced output to a Mainline and its balanced output splitting its signal to a Kaiju and a Stereomour II. I have music playing through the BeePre/Kaiju/Stereomour currently, but not the Mainline and decided to move the Mainline across the room. To do so, I unplugged one of the two input cables and when I did so my speakers developed a hum until I plugged it back in.

I'd expect that if I unplugged an input but not an output. Is that typical behavior or is that symptomatic of a problem?

[Paul Joppa]

Can you clarify?

* Neither Kaiju nor Stereomour  have balanced inputs, so how are you using the balanced out from the preamp?

* Did you mean you unplugged one channel between BPre and Mainline, or both channels?
(Related: does the Mainline have more than one source connected?)

* which end of the cable was unplugged?

[Jameson]

Sure thing, Paul.

• I have adapters from balanced to RCA.
• I unplugged one channel at the Mainline end. There is another cable connected to the other input (a 3.5mm to RCA cable) but nothing is connected to that.
• The Mainline end was unplugged

[Jameson]

Here's a shot of the RCA cables at the BeePre end if that helps

[Paul Birkeland]

I'd expect that if I unplugged an input but not an output. Is that typical behavior or is that symptomatic of a problem?

The unplugged cable becomes a big antenna that can pick up noise and present that at the inputs of your amplifiers. 

[Jameson]

Thanks, PB. It's a pretty long run of cable, too, so that tracks.

Mostly wanted to make sure I wasn't operating with some problem that would blow up into a much bigger problem later.