We had a high pitched squeal that only happened when the A/C was on, at highway speeds, and when raining. The squeal happened every minute or so and lasted about 5 seconds. I had to take a dealer tech on a road test during a thunderstorm to "confirm" the noise. The dealer replaced the A/C belt and all is quiet. No one could explain why. They also ended up covering a hole in the plastic underbody engine cover directly underneath the air conditioner in an attempt to keep this from happening again.