I have been fighting a loud hum or buzz sound in my dash camera recordings. I had finally found that if i didnt use the cars power , then there was no buzz. I have a 12v to 5v converter and a USB from the 5V to the camera. This device plugged in between the USB cable heading to the camera.
It totally stopped all hum and buzz sounds. There is now just a crystal clear sound of my radio or someone talking! It worked perfect. Your problem my be different than mine but for me, perfect!