Is anyone familliar with the Ferrite cores?

[rado84]

Are you sure it is the SW picking up the interference?

Well, it has to be. The speakers receive signal from the SW and convert it to sound. That buzz I hear comes from the speakers, so it has to be the SW. More than that, when I approach the phone to the SW (the speakers are about 2 meters from the SW), the buzz starts, so it must be the SW that picks the phone interference. On top of that the SW has an antenna for FM radio and I'm almost sure that antenna picks the signal up.