Why transformers create noise, how can reduced transformer hum

Transformer Noise
The"hum"caused by energized power transformer, under no-load conditions,originates in the core
where the laminations tend to vibrate by magnetic forces. The noise is transmitted  through the oil to the tank side and thence to the surroundings.

The following are the main factors which produce noise in transformers:

1. Magnetostriction (occurrence of dimensional changes both parallel to, and perpendicular to the direction of magnetisation)
2. The mechanical vibrations caused by the laminations, depending upon the tightness
of clamping, size, gauge, associated structural parts, etc.
3. The mechanical vibration of tank walls.
4. The damping.

The noise emission may be reduced by the following methods/means:

1. prevention of vibration of core-plate by the use of a lower flux density and giving
attention to constructional feature (such as clamping bolts, proportions and
dimensions of the 'steps' in plate width, tightness of clamping and uniformity of plates).
2. Using cushions, padding, or oil barriers to sound insulate the transformer from tank.
3. Designing suitably the tank and stiffeners to check tank wall vibration.
4. sound insulating the tank from the ground or surrounding air.
However, the noise problem cannot be solved completely.