No I have not noticed any knocking. But then, I had another issue where there was some chirping/squirrel type noise - similar to the old loose fan belt sound - that I could only hear with the window rolled down.
Im also told that the computer adjusts the timing so there isnt an issue. The car runs fine.
Ive test drove both the GS as well as the ATS and I do like the boost in power. If I had the extra power then Id run premium.