Help! HT3813 please help diagnose this engine sound 11/23/2017

FlyingAxblade

First published at 22:23 UTC on November 23rd, 2017.
    has

I finished mowing, was washing off the dog poo and it started knocking so I pulled it off the grass and filmed this.

CategoryAuto & Vehicles
SensitivityNormal - Content that is suitable for ages 13+