[Radio Wrangler]

THe wasps in a bean tin comment makes me wonder if you have a snare drum effect with a cabinet part vibrating in the field.

One trick is to wrap thick copper foil around the OUTSIDE of the lamination stack, over the bulge of the windings and to solder it as a 'shorted turn' around the outside of the transformer. Being on the outside, it doesn't muck with the main field in the transformer, but it does act to cancel stray field leaking out.

David