Audio Systems: Humming, electromagnetic interference, sound speakers

Question
I think that my av receiver has developed an permanent fault. I have a constant
humming on my front left and right surround sound speakers even when all of
the source input wiring has been disconnected. The amp is 5 years old and I've
never had any problems before.... have you any suggestions?

Answer
Have you isolated the issue to the receiver and not the speakers?  Try connecting speakers that don't have a hum to the output in question, also connect the humming speakers to the outputs that don't have a hum.  

If the hum follows the output and not the speaker UNPLUG your receiver open it up and blow all the dust out with a can of compressed air.  The dust could possibly be creating a short.  Don't be intimidated by opening up your equipment, just use common sense.

If the hum follows the speakers see if maybe a lamp cord  or some other electrical cord has has fallen on your speaker cable.  This would create electromagnetic interference, which would be an audible a 60hertz tone.