This is my first Mazda. Bought it new for daughter in Spring 2015. 20,000 miles on it now. Recently, noticed squealing noise on interstate travel beginning at around 75 mph and at 80 mph it is constant. It gets louder as you move your ear closer to the center of the front dash. Not sure if it is engine bay or within the dash itself. Sounds like morse code to begin with, long and short squeals, then becomes constant while cruising at 80. Doesn't sound like a wind noise. I though it was an electronic interference at first, but it still occurs with stereo off. Anyone have an educated guess on this?