Grain or noise is typically induced when one has a higher ISO and is not shooting using the proper frame rate and shutter speed.
You optimally want double the shutter speed of your frame rate.
So if shooting 30 frames per second you want a frame rate of 1/60th of a second. After setting these two parameters manually then adjust the exposure and see if you can properly expose the subject.
This is all in manual mode and not automatic. If you cannot adjust exposure to a proper level for the subject then add an ND filter to the Mavic Air and increase the density of the filter until you can expose the subject properly and maintain the double shutter speed of frame rate.