by the way I have tryed on several computers ...

with several cables ...

and I found that wich is the same problem but no solution
http://forums.techguy.org/networking/286779-laptop-makes-high-pitched-noise.html

2012/7/17 Roch Jub <rochjub@gmail.com>
hey !

so I have a weird problem here

On one laptop I had no line in, so I bought a behringer UCA202 wich is a line in to usb.

Now when I use it, in pure data, or audacity, but i'm sure other softwares,

it's working fine untill I plug the laptop to another laptop with just a RJ45 cable, no box.

As soon as the computers are connected, I have a terrible noise ... it's quite low, but it's very anoying.

Somebody ever had this problem ?

cheers