I have a Tempest driving original Stratos Monos (cap upgrade, but old circuitry) When the system is idling it makes a fairly low level 'spitting' noise. Actually sounds a little bit like one of those electric bug zappers. Not loud, and occurs maybe once a minute. There is also a low level 'hiss', but you have to be quite near the speaker to hear it.
Any thoughts? I thought maybe it was the cheap IC's I use on occasion to listen to DVD, but that's not it.