....do these actually make a difference? Do you think it's worth getting one? The reason I ask is because last night my speakers emitted a fairly loud low pitched hum, followed by another. Now although my amplifier was switched on, all devices connected to it were switched off, even the volume was turned all the way down on the amplifier. So I'm atttributing this noise to some strange power surge (I live in an old house I suppose). A standard surge protector would probably stop this, but if I'm getting one of these I might as well pay a little extra and get one of the special one's that filter out dirty power and claim to improve the sound. Where can I buy one of these?