Since 27K miles, we've had a mysterious and sporadic chirping or whistling noise from inside the cabin. Hard to even identify source as front vs. rear; left vs. right. Lasts only a split second, but can occur up to 10x per hour. Happens whether moving or idle at a traffic light. Dealer can't find the source. Seems to me like a spring clamp, cable or pneumatic release that occurs which involves some friction that translates to a short, chirping noise. Any ideas or clues would be most appreciated!