How do you stop transformer hum?

1. THE INSULATION IS DETERIORATING

2. LOOSE TERMINATIONS

3. NO RUBBER FOOTING INSTALLED

4. OVERLOADING / UNBALANCED LOADING

5. Magnetostriction. When the core becomes magnetised, it expands, then it contracts and expands again as the field is reversed. A 50Hz transformer therefore expands and contracts at 100Hz, producing a sound at that frequency.