Funny you should mention this now.
Got a Petro Canada Car was season pass for the winter, and I noticed a bit of flutter when I was passing though the super duty driers at the end.
Didn't think anything of it, becuase I remember Chris Harris' S4 doing the same thing.
I will try to remember to take a video next time I'm in there and post it. See if it is similar to what you experience.
On my track day, no issues.