Though this sounds quite low for a plane, it is quieter than a helicopter flying at the same altitude as the plane has been specially designed for noise reduction. If someone is standing directly underneath it, the volume is like that of a blender running in your kitchen, or a passing vehicle going at 50 km/h.
Bell Geospace have an unblemished safety record and the Basler BT-67 plane has a strong record of reliability.
The video below shows the plane flying over a horse and rider in Cornwall from a first-person perspective. The plane here is at an altitude of 100m.