Our thermostat regulates AC/heat pump. Early this morning, it started
buzzing rather loudly while on the "heat" setting. It had been on the
same setting all night and started buzzing spontaneously. I thought it
might stop on it's own, but after about a minute I adjusted it - thought
I had moved the button to "off" but it was dark and I had switched it to
"emer heat" which stopped the buzzing. It's never done this and I am
puzzled as to what might have caused the noise.