➽ The basic cause of transformer noise is magnetostriction.
➽ There is expansion and contraction of the iron core due to the magnetic effect of alternation current flowing through the transformer coils.
➽ The magnetic sheet steel extended when magnetized again it goes back to its original condition as the magnetization is taken out.
➽This produces an audible hum.
➽Magnetostriction may be partially controlled by the transformer design, but it cannot be totally eliminated.
