Three queries about ArduPlane on the Omnibus F4 Pro

omnibusf4pro 0030004D 3548500A 20373753
ChibiOS: d2030d88
ArduPlane V3.9.7 (6a3513fb)

I have an Omnibus F4 Pro ver3 FC board that I am setting up on the bench. Everything is working fine so far, but I have some queries.

Q 1. The Omnibus F4 Pro uses a buzzer like this:
which just requires 5V to make a 2khz noise/whistle.

When I first connect the battery to the FC, the buzzer emits a loud 2khz tone for several seconds while the FC is booting up and then emits the usual ArduPilot musical tones to indicate that it is ready. I would like to know if there is any way that I can make the buzzer be quiet until the musical tones are emitted? I am guessing that the buzzer port is being held at +5V during the boot up stage and thus causes the continuous tone for several seconds?

Q 2. To calibrate the current sensor, I connected a 4.2 ohm/40W resistor where the ESC will be powered. At 12 V, this should draw about 2.8A in addition to the quiescent current (~ 0.5A). However, the reading that is displayed in Mission Planner fluctuates rapidly between about 3.1A to 3.5A. When I view the battery current in the log file, this is what I see:

which shows that the current reading is very noisy.

Is this noise due to sampling errors in the F4 ADC? And is there any way to reduce or eliminate that noise?

Q 3. I get an error message in Mission Planner that says “Bad or No Terrain Data” when the SD card is not inserted. That message seems odd and probably should say something more relevant like “SD card not detected”? Is that correct?