So, if you were to relieve the pressure on the PTO Pump, put a coupler across it, does it change the vibration? I guess I am getting at is how you get to wether it is like on a car... if you feel the issue under acceleration it is engine or tranny, and if you feel it under coast it is the wheels. Wondering if you can free-wheel your pumps, and see if the vibration continues. I would assume, probably incorrectly, that a pump with no load would have less chance of vibration than one under load.