Investigation Doncaster Yorkshire UK - Talking speaker.

This incredible event happened at a working mans Club and occurred when I was setting up my equipment. The Club had a number of PA speakers and monitors on the stage and whilst I was busy setting up the gear a voice emitted from one of the stage monitors which was a few feet away, very loud and the voices heard sounded like people chattering. The monitor where the sound was coming from was neither connected to the mains or any input, nothing was plugged into it. It was also a passive speaker which needed an amplified signal anyway and not a single wire or lead was connected, and I promise you, I checked that monitor over and the more I couldn't find the answer the closer I looked. The voices stopped once I got hold of this 100 watt monitor speaker and never returned. I was fortunate that two other guys were present and witnessed this strange event which left us baffled. Unexplained.