Gidday Jack ,MF and all,
I'm sure the scientists would use an exhaust gas extractor when testing petrol engines.

Engine noise was just one problem , it's easy just to install a quieter muffler so the electric motor is not going to
help with objectionable noise levels generated by the motion of the cutting blades themselves.
This weekend one of my neighbours was mowing his lawn he was 50 meters away from me,he was using a newish mower
and I could barely hear the noise from the petrol engine but I could not believe how loud the blade noise was from 50
meters away.
The loud exhaust on a lot of mowers will drown out the blade noise.
If all else fails I read the manual

Cheers
Max.