That noise is almost certainly because of the inverter.
Take a piece of wire, and attach it to a bit of bare metal on the casing of your power supply. Run this to the same ground as the rest of your audio equipment - especially the inverter.
The Lilliput flickering is probably because of the engine running, and it not being regulated power.
To fully fix both problems, get yourself an Opus power supply, and wire the screen directly into the Opus
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