Khandro, perhaps you really aren't aware of the difference between sound waves and radio waves. Sound waves can only occur in a material medium, ie. solid, liquid or gas. Radio waves on the other hand are part of the electromagnetic spectrum and do not require any medium for their transmission. They behave entirely differently to sound waves, why not look them up on wiki.
The sounds you hear on your multidude of electronic devices are not a conduit for sound but converters of electromagnetic radiation into sound waves. The idea that radios receive sound is rather naive, they don't. The reason you cannot hear any sounds when you switch off your electronic devices is because there are no sounds that you can hear. There will certainly be sounds outside your range of hearing (both frequency and amplitude).