Whistling sound while driving?

I am hearing a high pitch whistling like sound while I drive my vehicle. The sound is not there when the car is not in motion, idling or If I touch the brakes while driving. The whistling is sometimes constant for a length of time and then will be intermittent at times. The sound doesn't seem to get worse or louder with speed changes, It's just very random. It also doesn't seem to make a difference if I am turning one way or the other or not at all. Sounds like it is coming from the wheel area not the engine. The car is driving fine. Any idea what this could be?