Techie stock transformer and hum: two questions

[Epicurus]

OK, I've read on various sources that the Techie's stock transformer hums audibly. I actually experience this issue. So, here are two questions:

1. Why does it happen (even though it's shielded in an aluminium box)?
2. Short of resorting to an external PSU, what can be done to stop it?

[Reid Malenfant]

1. Possible vibration getting into the Technics chassis & it acting as a sound board.

1. Possible loose windings causing them to vibrate & thus produce sound.

1. Possible loose laminations, read above

2. Remove the transformer, place it in a box (or possibly use the aluminium standard one) & either fill with potting compound & leave it to set, or varnish & oven bake preferably after vacuum impregnation