I read that in xformer its due to magnetostiction.
1. How to reduce it.
2. Then why there is noise in poles & wires carrying higher current & voltages.
3. When neutral is eartherned at xformer site, then why there is 2V around b/w neutral & earth at house.

 

A cheap transformer has loose parts that vibrate in its laminated core.
A high quality transformer has its laminations held together with enamel so they do not vibrate.

The neutral wire carries current so it has a voltage drop.

 

Thnx Audioguru,

1. But there is hmm. sound near big transformer at power station also.
2. Also why wires having high voltage also produce niose. Why is it so??????

 

A big transformer produces hum because the AC current in it causes it to vibrate due to magnetostriction.
High voltage wires buzz due to sparks leaking out of them.

 

Also in a transformer the magnetic field exerts force on the windings, so if they are not potted tight they will vibrate too. But this is not magnetostriction, it is due to Lorentz force.
You can´t really avoid magnetostriction in the core, you can only choose materials in which it is lower.
Neutral to ground voltage is caused by the current flowing through the neutral, so there is some I*R drop on this line, while in normal situations no current should be flowing through the ground wire.