Q: Car whistling and shaking when driving and running the AC

Greetings! I will be happy to help. Your description leads me to believe that both of your issues could relate to your serpentine belt. The belt wears out over time, and will at times try to notify the driver of an issue by making a whistling or a squeaking sound. The AC system is belt-driven, so an issue with the belt could cause problems in its performance, such as a shake. However, most of the AC system’s vibrations should be absorbed by the motor mounts, so you should not be experiencing too much shake behind the steering wheel, unless the motor mounts are faulty. Therefore, I also suggest checking the motor mounts for wear and deterioration; factory motor mounts are made of rubber and the rubber insulation becomes brittle over time.

A good place to start is by having a certified mechanic, such as one from YourMechanic, come out to the location of your Pontiac to run an inspection on your AC system, and replace your serpentine belt, if deemed necessary.