Increase PWM frequency
SammysHP: The PWM is fast on purpose. Slow PWM is really annoying to people who can see it. Like 2.5 kHz looks like a bad strobe light. I generally try to get it close to 20 kHz. High enough that people won't see or hear it, but no faster than necessary.
Currently this firmware uses ~2.5 kHz for better 7135 efficiency. Maybe this is too slow.
When increasing the frequency it is important that the on-time is above 8 µs so that the regulator can fully turn on. Maybe it helps to change the frequency together with the duty cycle.