Well....It doesn't get much better than this for pattern observation.
Some good findings: I drove for 30 minutes in a combination of highway and street, mild and strong acceleration, up and down hill.
ALL BUT ONE OF THE OCCURRENCES HAPPENED AT THE SAME RPM (~1,200) AND SPEED (~52 MPH). The last occurrence was the only one that happened at a lower speed (<40mph) but it is also the only one that happened while I was turning.
Anyone pursuing this, please feel free to share or re-post the video (contains only the occurrences - everything else is edited out).
wk4 Summit noise - YouTube