Interesting. I also do hear a "strange" oscillating sound occasionally shortly after startup. First I thought it comes from the speakers, but it isn't I think. I'm starting to suspect it has something to do with me activating PSE and Sport right after startup. Sound actuator is a possibility as well for sure. It doesn't happen frequently enough to really bother me and never when the car is warm so far. But after reading your post I'll keep watching if it becomes more frequent.