Airport Express Hum only when AirTunes is not playing

Question

Hi,
I have an Airport Express, the Airport Admin Utility says it is Apple Base Station V6.3 (I presume that's the firmware version).
As long as AirTunes is streaming music to it, it works fine, but as soon as AirTunes stops streaming, there is a barely audible 60Hz hum (you have to be within 2 feet of the speaker to be able to hear it).
If I stream complete silence to it (I made a silent track with GarageBand to check this) there is no hum (there is a very faint white noise though, not sure if I like it much better than the hum).
So my suspicion is that if there is nothing streamed to AirPort, it lets its output go "open loop" and then the two feet of cable picks up the 60Hz from the electrical wiring in my house. It's similar to just connect an audio cable to your amp and leaving the other end just lying around, not plugging into any audio device.
Is there a patch/firmware update that would always keep the output "closed loop" if nothing is streaming to it?

Answer 1

thing I can think of is to change the source on the preamp (for instance
if Airtunes is on Aux, I push Tuner or Disc) when I have finished with
Airtune and want some silence...
Interesting work-around. Unfortunately it won't work for me because I plugged AirPort Express directly into my poweramp .. left-over from my purist days when I didn't want a preamp sitting between the music and the poweramp
Good to hear someone else has the problem, I hope someone from Apple could chime in whether a firmware change to "close the loop when not streaming" is technically possible, or if there is any other type of solution.