If it was a synthesiser you would think it was a stuck key. Continuous
cyclic racket, sounding like a swarm of hornets, mosquitos and bagpipes
with chorus effect thrown in. Presumably DSP problem. Changing buttons
etc changes the character of the noise and the display functions
normally. Only got in far enough to see a RED LED flashing fast and
regular but slightly modulated I think, and noise does not vary with
twizzling.
I'll take a recording of it before full disassemly, in case it is
diagnostic