rear defrost buzzes until I push it
 

Ever since I got this 1987 rx7 when I start the car I hear a buzzing sound. It took about an hour of pushing buttons. Finally I hit the rear defrost button and the buzzing stops. Any idea of how to fix this. My dash lights don't work either. My turn signal in the dash works and my brake light in the center display works. Other than that I have no illumination. Thanks in advance for any help.