Noise in recording

[MikeTenFive]

I've just installed the latest version of WavePad from the NCH website.

 

I have two computers, virtually identically configured, standing next to each other. I use an external sound card that takes audio output from a musical instrument and passes it to the computer via USB cable.

 

I have found after repeated testing that if I record audio one one computer I consistently get static noise mixed with the music all through the recording, but if I plug the same devices into the other computer, standing right beside it, I get clean recording.

 

Same hardware (virtually), software, input device, electrical environment.

 

Where's the static noise coming from?

 

(I know it is NOT the fault of the WavePad software, but I was hoping somebody with some technical expertise could suggest something.)

 

Thanks!