I have a 9VAC GE security system transformer that began to make a faint buzzing sound and I'm worried this may be unsafe. The noise started a week ago after several weeks of it *not* buzzing when first installed - or at least I never noticed it. The unit does *not* appear "hot".
I changed the receptacle that it is plugged into and checked for grounding and it is properly grounded. I tested the voltage for 110v with a multimeter and it is steady at 110. I also swapped the transformer with a new one but it still buzzes. Finally, I ran the transformer to another two outlets and it buzzed on both, but each with different intensity.
What could be the cause of this, and how do I fix it? Is this a warning that it should not be used or corrected?