Aesthetix Io strange behaviour

This morning, my Io won't play music. The only thing I hear is scratching/popping noise when I turn the volume controls. Same thing in both channels. Tried changing cables, etc, but no change. Anyone has an idea? The unit has played beautifully especially since I got a full tube replacement from Aesthetix some years ago. I've heard nothing to indicate a coming breakdown. The lights on the unit come on OK, and as far as I can see, the tubes light up normally too. Strange.