Why do I get background noise after using PsychPortAudio?

Hello,

I am using PsychPortAudio (PsychToolBox) to play some sounds. Sometimes, after running my code, I got background noise in any sound I am playing on my computer (not only in MATLAB). Why could this be? I wonder if, somehow, the channel I create remains open, but I used the function "PsychPortAudio('Close')" and I did not get any warning, so I assume it is working correctly. I managed to solve it through the sounds settings of my computer, but I would like to prevent this from happening again.

Any idea would be highly appreciated!

Laura