I have found and put into practice a little plugin script for Audacity to generate tone sweeps.
Whether I listen this from my iMac->headphone out->little H/K speakers
I hear the same "artifacts" if played with Audacity or VLC:
Approx. from 1.5 to 3-5 seconds I'd describe the sound as oscillating from left to right
Approx. from 8.5 seconds onwards the frequency sweep is also piggybacked by apparently random oscillations similar to old radios being tuned.
What's happening ?
I am not hearing these artifacts if I play the same file via Audirvana or even if I drag and drop it on the browser
Here is the file: http://www.filedropper.com/sweep
Thanks a lot