What causes a high pitched noise while driving on the freeway?

More than likey, you have wheel bearing staring to fail. A test drive by a competent mechanic may be in your best interest.

Great description! The noise you have described can come from a few different areas. It could be tires that have abnormal wear, brakes rotors, disc pads and/or bearings. It would require a complete diagnosis to pinpoint the exact source and the proper repair procedure. This testing runs $ 39.95 and is no charge with repairs.