Do the speakers flicker when the copper cable is on?

Question

Acustic systems

Hello!
Please tell me how to solve the problem.
There is acoustics 2.1, the amplifier is built in a subwoofer. It has two RCA audio inputs. One input includes a wire from a media player, the other from a computer of the Jack 3.5 to 2-RCA type. The wire from the media player is ordinary, and from the computer it is copper (I bought it specially expensive, hoping for better quality).
In general, when the computer is turned off, loud background noise comes from the speakers, but as soon as I disconnect this copper wire, the background stops. I tried to connect a regular cable to the computer - there are no such noises from it, everything is quiet.
This copper wire cannot be replaced, because I was looking for a specially 15 meter one and already scored it under the baseboard, I will have to tear off all the baseboards.
Is there any other solution to the problem, what to do with this wire?

Answer 1

It is logical to assume that something is phoning on the cable. That is, next to this cable should not go other cables, especially power supplies.

Answer 2

You said that when the computer is turned off, there is noise. What if the computer is on? is there noise?

Answer 3

Is the cable shielded?