(Technically speaking, it's been there with 2 different motherboards, 3 different dedicated soundcards and onboard sound, 3 different mice and 3 different versions of windows (7, 8.1 and now 10) and no change..)
Using my Yamaha hs50m connected via rca to the asus xonar essence stx, I have a high pitched sound being emitted in perfect "harmony" with the cursor movement.
There's also a fairly high level of ground noise that annoys me when no music is playing.
I recently added a headphone amp to the collection (also connected via rca) and there the interference is even worse!
I'll have to check again whether the amplified headphone out shows this too, haven't tried that in a while..
I saw that others had this issue 10 years ago already, so it's not something simple to get rid off, I guess?