Sorry about that ...If I cut the power, I just might be living alone.
You could try the test without cutting off all the power. Obviously, you need lights there and if the HVAC is essential then keep it going, just try and switch off as many as the other circuits as possible. Note that the system doesn't have to be run hard during the test listening.
The system could easily be solid enough to give a good result without going all the way.
The key ingredients are fully stabilising the components, in a minimum configuration, switching everything off, flipping the switches, etc, and switching on again, and listening carefully during the first half hour. That may give you enough clues, and is worth pursuing ...
Anyone else lurking, are you game, willing to give it a go? Roll up, roll up, tuppence a throw ...
Frank