[Dan Banquer]

I decided to do some experiments with the squeezebox and it's wall wart. I wrapped adhesive copper foil around 85% of the wall wart and soldered a wire to the adhesive copper shield and then connected the wire to earth. This did nothing. ( Remember, I am using my AM tuner as my "meter" for the interference.) I then proceeded to disconnect the wall wart from the squeezebox but leaving the wall wart plugged into the AC line. This reduced the interference dramatically but not completely. I then plugged the wall wart supply back into the squeezebox and disconnected the spdif to the rest of my system and the interference disappeared.
So my conclusion is that radiated interference is not much of an issue, but the squeezebox conducting noise through the grounds is the issue. This appears to speak volumes about the squeezebox/wall wart grounding.
Anyone else have any educated guesses?
           d.b.

[inguz]

I added a couple of chunky ferrite rings around the wall-wart's cable; one at each end.  This seemed to completely remove the RFI I'd experienced at the power amplifier (based on listening - I don't have an AM radio or a RF oscilloscope...).

So I'm happy with my guess/preconception/theory that the cable, more so than the SB or wallwart, is the interference radiator.  It would be interesting to hear if you get similar results.

[inguz]

And... I do think the wallwart dumps hash into the mains (which sounds like exactly what you're suggesting).  In my case the only other piece of audio equipment is a power-amp which has extreme overkill filtering on its power supply stages, so I think most of my noise sources are radio- rather than ground-coupled.

[Dan Banquer]

The squeezebox wall wart is plugged into the third bank of a Tripplite Isobar Ultra so that is not the issue. The Tripplite has some pretty brutal HF filtering. (Some folks have strong objections to the Tripplite, but I have had nothing but positive results with them.) I took a trip to Radio Shack ,and purchased an optical cable to connect the SPDIF instead of the coax I was using and the problem has been solved. If your problem is a grounding issue, which it certainly appears that way from my experiments, then the optical cable will break the ground connection.
If I get some time this winter I will build a linear supply for the squeezebox and we will take it from there.
             d.b.