Please see: Libre Computer Board Composite Video Pinout
You can purchase the adapter from here: CVBS Adapter for AML-S905X-CC-V1.0A and ALL-H3-CC-H5-V1.0A/V1.1A. – LoveRPi
There’s a MUTE GPIO on the schematic to turn on and off the amplifier. You can manually toggle it to see if that affects the popping noise.