Excellent box! But perhaps the logo biases me
The problem is caused by your low starting voltage... the 12v up converter has a long way to reach to get from 4.8v to 12v and the current mode noise is going to be significant. A better option would be to start at 12v and then down convert for the transmitter.
When I used to use the PT5041 it was in a system rated to run at 8 to 11v.... the upconverted 12v went to a 12v transmitter and then I used a linear regulator to down convert for the camera. The jump from 8v to 12v is smaller so taming the noise was easier.
Hope that helps.
Bill