David Clark Headset Parts What Is Wrong With My David Clark Headset?

What is wrong with my David Clark headset? - david clark headset parts

I have a brand new headset David Clark 10-76. I also have a military, an adapter for general aviation. It is my intention to speak to others in the good air, but when the tour touching the ground or Unicom frequency that I hear made a piercing sound. What could be the problem? Thank you in advance.