Why do I need to yell to activate the microphone of the aviation headset,pilot headset,aircraft headset?

Why do I need to yell to activate the microphone of the aviation headset,pilot headset,aircraft headset?

Your avionics’ squelch setting may need to be adjusted. It is common for pilots especial for student pilot to change the squelch setting just like adjusting the volume. Please consult someone who is familiar with your airplane’s avionics if you cannot locate the squelch knob or button. Also, make sure the mic is close to your lips. The closer it is, the better it will transmit without raising your voice.

How to set squelch adjustment control in your cockpit? 

If you can find the squelch control please adjust this control. The sensitivity of the squelch is controlled by turning the control clockwise (increasing mic sensitivity) or by turning the control counter clockwise (decreasing mic sensitivity). The squelch can be adjusted to meet even the most extreme noise levels of aircraft noise. 

Setting the squelch properly allows the intercom to be active only when someone speaks into the headset microphone and the intercom will become inactive as soon as they stop speaking. In this manner, all extraneous noise in the cockpit is not heard over the microphone of your aviation headsets.