The sound you are hearing when you switch on your AVANT or any CRT TV is the "Degaussing Coils" around the tube energising for a couple of seconds. If you did not have this "Degaussing" then you would find parts of the picture deformed or a particular colour showing in one corner.
When you switch off your TV it is not possible to reduce the magnetic field around the tube completely to zero, so this degaussing process eliminates this unwanted magnetic field and subsequently allow you AVANT to function correctly.