I think Charlie is right. I thought you have the problem only if you run SONAR. If the sound is there while playing tracks from e.g. the media player, it should be a ground problem.
If you are sure that you changed nothing at your setup, then use a power extension and try an outlet with another fuse. Probably a new coffee maker or something else in your house is the root of all evil (noise)...
 
(VDD).
You thought absolutely right. I ONLY hear the sound when I run sonar. And just when I open a project or new project. I mean in the start page of sonar I don't  hear the noise, it just happens right after opening a project even new.
I don't hear the noise with the other players like windows media player . they are fine.
So it must be something belongs to sonar.