Try standing in front of the engine and listening for it and then stand behind the engine and listen for it. Like the Doppler Effect, you should hear it louder on one end or the other. Try disengaging your manual pto lever once it is running. Chances are it is in your front pto and it could just be the wear button.
EDIT: OOppsss......ignore my comment. I just re-read your post and realized that you have your pto removed from your engine so it cannot be that.
Cub Cadet 123
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Still don't know what I'm doing in OHIO?.....If you find me, then please point me back toward INDIANA. 
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