Hello guys, here's another one for you.

I have an old (like most stuff in the house I live in) NuTone musical door chime. It is electronic and you can select several different songs. It has a speaker like you would find in a radio or stereo. It is a two button (two door) chime. It is fed from a Rittenhouse RT34 transformer attached to the electric panel in the basement.

The chime started making a very loud humming/buzzing sound, coming from the speaker of the chime.

The noise occurs when both door buttons are disconnected. The noise stops when I cut power to the circuit with the circuit breaker, and when I disconnect the DC wire in the chime itself.

The question is, how do I determine if the transformer is bad, or the electronic chime is bad? Thanks.