@g-ferrando You can safely ignore that message.
PX4 doesn't have any filters on the power rail of the ADC so it flags any bit of noise on the 5V power rail. We've taken steps to improve that on FCv2.
On both FCv1, and FCv2, our hardware can operate much lower than that default PX4 warning. If you use our power module and get reports that way of system voltage and current using the I2C bus, you can trust those numbers.
Hope that helps.
G