Dave Plowman (News) wrote:
In article ,
N. Thornton wrote:
The problem is a design one. Almost all suggestions have been right
off track. Theres nothing you can do about it unless you mod the
design on the audio side, or buy some decent kit.

You can buy plug in mains filters.

This is uk.d-i-y not sci.electronics.

It would be sad to exclude simple electronics.

However, it would help the the OP actually read the replies and
answered the points arising.

If the same thing happens when using headphones direct from the
computer, then I doubt external filtering on its supply will help. But
if it stops, then the fault lies with the external sound system.

I get exactly the same on my computer speakers, it's especially evident
when the humidistat fan in the bathroom spends 20 seconds or so deciding
whether or not to switch off.

If I put my hand near, or touch, the very thin (2mm maybe) signal cable
which takes the audio from PC to speakers while this is happening, then
the effect stops. If I remove the signal cable from the speakers, the
effect stops.

The cable is basically acting as an aerial!

I keep meaning to either replace the cable with one with better quality
screening, or maybe put a ferrite core on it. But it's not a major
problem.