Ok thanks for the suggestions.
1) Removed the starter and turned the engine over with some rope on the cup. Noise was still present so that eliminated that cause.
2) Replaced the spark plug and gasket in case of damage and no change.
3) Check the cowling to ensure no bolts were rubbing up against the flywheel.
4) Confirmed nothing was caught underneath the base of the mower.
I kept hunting around and pretty much confirmed it was some sort of sharp air leak contributing to the sound. Every time you pull the rope with the mower in the stop position you could hear the hissing sound. I ended up finding an air leak on the exhaust side just by feeling around the area whilst pulling the rope. (engine had to be cold of course) A sharp burst of air seems to be leaking out the exhaust gasket.
I�ll have to take it off tonight to take a better look. When I removed it the first time it only had the soft heat shield/soft gasket between the exhaust and engine block. A pretty standard set up for these Chonda�s in my experience.
Does it sound like I am on the right track?
