G'day Tiger, you have eliminated the coil being the cause of the grinding noise.
Those utility mowers can be treated pretty poorly, so crank being bent is a possibility.
To investigate:
Remove spark plug lead.
Remove the blade plate.
Look to see if the crank is baldy bent by rotating the engine, you should notice a badly bent crank with your eyes.
Use your senses to try and find the noise.
You can detect a slightly bent crank using a dial gauge or clamp something close to the crank shaft, rotate the engine whilst noticing the gap.
While your there, grab the crank and check it for movement. Your noise could be bearing related.
