How can just the test lead alone. Un connected to anything ,cause subwoofer to pop ? To me seems same as adding 24" of wire to hot connection. Same reaction with bare tip on screwdriver, etc.. Built in amp causeing some kind mag. Field? Antana type ?

You have just created a 60 Hz transmitter.

When a hot and a neutral run near each other or in a metal box some amount of shielding or cancellation takes place.

Every mains wired house has an electromagnetic field radiated from the mains wiring. If you're in the USA it will be at 60Hz, or in the 'civilised' :-) world, 50Hz.

Any piece of metal (wire, screwdriver blade) acts as an antenna and picks up that 50/60Hz radiation (and a lot of its harmonics). So when you touch such an antenna to an audio amplifier input, the picked-up 'buzz' (fundamental plus harmonics) is amplified and makes a sound in the speaker.

Daniel