Lighting, Light Fixtures, Ceiling and Exhaust Fans - Ceiling fan/doorbell interference

I recently installed a low voltage electronic doorbell. Because it was going in anew, more central location, I put in a new 24 volt transformer, in the attic, just above the bell. I mounted the transformer to an existing j-box, with a circuit serving the attic light, and some other loads, including a ceiling fan.

When the ceiling fan is turned on, the doorbell operates. Strangely enough, the same thing happens when either of the ceiling fans on the next circuit over (which shares a neutral) is turned on.

The ceiling fans are a variety of brands, without light kits, and are each controlled by a Hunter, 3 speed switch.

I have checked and re-tightened all the wire nuts and grounding in the two circuits involved, but note that none of the fan switches are grounded.

I am stumped.

Did you connect the ceiling wire to a 120 volt course, or is it connected to a wire directly feeding a fan, which won't necessarily be 120 volts, since the fan has a speed control?

Either way, it sounds like you need to find a different place to mount the transformer.

Transformer is wired directly to a 120 volt circuit, not a switch legs. Fans are standard Hunter and otehr big box supplied units

Which wires in the box did you hook the transformer to?

Try using an electrical tester, and determine if the wires that you are hooked to have 120 volts regardless of any of the switch positions.