Static noise from speakers when computer is off

"Actually, when you turn a computer off, it's not always completely off, just more in some kind of ""standby"" modus. Ever had an USB light connected to your computer? Did it go out when you turned your computer off? How about the lights at the back for your network card? (Some have lights there!) Are they off too, or does it support a wake-up call from the network?
Keep the cable connected to your speaker, but plug them out of your computer. If you still get noise, the cable is the problem. Otherwise, the computer still generates noise even though it's supposedly off."

I had this same problem and fixed it by moving my wireless router further away from my sub-woofer. Not too sure why but it's fixed the problem.

"What ground are you connected to?

Is your power outlets grounded?

No ground at all can also cause this type of problem, since you can become more receptive towards external noise."

"""Static"" noise is not a hum but a scratchy noise of varying amplitude and frequency.

50/60 Hz induced hum from power run around the place is possible from the description but that's a lot different from the ""static"" described.

On the other hand that noise continues when the amp is disconnected is quite possible as the capacitors in the circuit may hold charge for some time after switch off, operating the amplifier at a reduced level and perhaps amplifying induced noise or connector resistance noise.

If this noise continues for longer than say ten minutes it's unlikely to be from the disconnected amplifier (and is the amp actually turned -off?"" and likely to be induced from some nearby source such as a switch mode power supply or some noise being fed into the mains from some source, perhaps not even at your house, and radiating.It's possible but unlikely that metal dust is caught between magnet and cone.

Finally noise from poor battery connections in the amplifier or poor speaker connections or the amplifier acting as a low level transmitter through poor feedback design, say, are other possibilities.

Cheers, Jack"