That is the low rotor rpm horn. You need to be at full throttle to let the governor take control.
Power is your collective setting, rpm is your engine percent. Watch your tachometer (upper right gauge) and you can see that you are in the lower end of the arc and that is why the horn is going off.
The governor is off by default, which it shouldn’t be, because there is not a switch in the cockpit to turn it on. You have to set a key bind or button to turn it on as a work-around.
edit: search for ‘governor’ in the controller settings. It’s best to set a bind to ‘governor on’ and ‘governor off’. This way you know for sure what state it is in, rather than assigning ‘governor toggle’.
The yellow light on the panel is the ‘low rotor rpm’ warning. The red light is ‘main rotor gearbox over pressure’. You’re pulling too much collective.
vote for the bug here: