Ultratherm UTH's buzzing?

So I was doing some checks before I went to work today I bent down to make sure both probes were firmly between the cage and the UTH and as I came up the pad under the top cage made a soft buzzing sound, as did the UTH on it's other side hooked into a rheostat as a temporary fix.


The empty cage beneath it did make that sound. It was so soft and quiet I began to wonder if it was all in my head.



This happen to anyone else? My heat pads are on a metal neodesha rack with a sheet of hand cut polyurethane insulation between them and the rack. And the heatpad between the insulation and the cage.


Should I call RB and See if this is safe?

They will buzz when hooked to a rheostat or a proportional thermostat (when the proportional thermostat is applying less than 100% power). I had the same problem when I had my ultratherms hooked up to my metal Freedom Breeder rack. Changing the t-stat to a grounded one solved the problem.

Heating elements have a high resistance factor. Applying a rheostat or proportional t-stat changes the resistance.

Try this: un-plug the UTH from the rheostat and plug it directly into the wall. Is it still buzzing?