Transformer hum?

Sugar --

Thanks for the suggestion. I would eventually like
to have a few dedicated AC lines run so the amps can get plenty of AC. Why does the transformer hum if it is
working extra hard? Can you explain that further? Also, how does dirty AC make the transformer hum and why doesn't
the AC conditioner, BPT-3.5 -- eliminate the hum when
components are plugged into it?

Transformers work because the expanding and contracting magnetic fields in the primary windings created from the changing primary currents cut through the secondary windings and induce current flow.

Transformers are designed to operate with a pure sinusoidal waveform. The current swings very smoothly from positive to negative with no abrupt transitions. This means that the magnetic fields are also expanding and contracting very smoothly. If you were to apply a non-sinusoidal wave like a square wave to most power transformers they would hum loudly due to the violent transitions of the current and magnetic fields. Any deviation from a pure sine wave can potentially cause these transformers to hum.

A dimmer works by chopping off part of the AC cycle and this produces noise spikes which travel through the system, and when they get to the transformer they cause it to vibrate. Not as much as a square wave but the principle is the same.

To see if the dimmer switch is the cause, go to your AC panel and find the circuit that the dimmer is on and turn that circuit off. If the hum is gone--there is your problem--if not look elsewhere.