A Ghost in the System? Music Thru Speakers with Preamp Disconnected

I disconnected my preamp yesterday completely from my system in order to install some constrained layer damping tape.  The DAC was on and receiving music, but the signal chain between the power amp and the dac was completely broken due to the preamp being removed.  BUT:  I could hear very low volume, but very clear, music playing thru the speakers!  And no, I was not intoxicated.  How is this possible?  Cool stuff.  Thanks.
Question #1: did the music audible through the speakers match the music being received by the DAC?  Whether or not it was the same will affect the diagnostic.
Were you hearing the same music that was on the DAC?  If not, probably RF interference from a local radio station.

By disconnected, do you mean you removed the interconnect cables?

If yes, then power issue. If not, you are getting crosstalk from the preamp, though it is usually thought of as a Left to Right thing, it's also possible to get it from one input pair to another.
This can only be Phantom Doppler Effect. You are moving so quickly that the sound is only catching up after you disconnected... 
Electrons move very slowing. So, after you pull the plug they’re already on the way. They just take a while to get there. 
Your entire system is possessed & likely evil. I'll take it off your hands :-) (You're Welcome) 
Music heard was same as that on DAC. XLR cables were hanging from the power amp and dac, but not connected together.  Preamp was unplugged and in another room!
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Stuff like this happens all the time. For some reason though it tends not to be reported until April 1st.
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Granted it is not easy to tell the April Fool’s from the normal everyday variety. I have to work very hard at it. One even has a whole entire website, a veritable shrine, the Las Vegas of Fool’s. But I can’t complain. At least not today. The other 364 days though....
This reminded me of something that really truly happens with my system. I don’t think it matters but I have a Denon AVR 4806 ~10 yrs old & we have outside speakers.  Although no one is allowed to touch it, once a yr sound starts coming out of the outside volume switch. It’s very faint & you can feel the switch plate vibrating a little.  A call to my stereo store & after some... push that, turn that switch all the way to the right & then flip that toggle down twice & once up... its gone. So, can some kind circuit  or set of wires, in the volume switch, vibrate when you “cross the streams” & cause that sound?  It’s usually the radio or what I’m trying to play outside from my iTv iTunes.
Well, you have either of two choices. It's coupled through the AC, or it's RFI/EMI coupled.

Try removing the interconnects altogether. They may be acting as antennas. Next, attempt to move the DAC closer and further away. You should get louder, or softer.

If neither has an effect, it's coupled through the AC power line. I suggest you split your devices up by either using multiple good strips like this Furman:


Or use a more advanced unit with multiple filter blocks. Furman, Shunyata and others.