Constrained layer damping tape on toroidal transformer?

Uh, the transformer is not “live”.

Siri, how does electromagnetic energy transfer work ...

@geoffkait is right, but don't use anything conductive!

No.

You could insulate the transformer, causing it to heat up, and the conductor itself could have currents forced in it, causing it to heat and melt.

If you are trying to reduce physical hum, better to look at the mounting method and eliminate DC on the AC line.

Best,
E