I just asked her if it ever does it for her while traveling straight. She said yes. Most often right after a turn while accelerating. She said, "Yes, I'm done turning and going straight again...picking up speed and 'clunk'."
I personally only experienced it when I was turning. It was like a subtle thump as if someone was tapping on something with a rubber mallet. It did it two times (Thump Thump) when I was turning left, and it would thump once when I was straightening the wheel after a right hand turn. But she obviously drives it all the time and I only took it for a 5 minute test drive.