Not sure if this has anything to do with it but at the boat show I saw all Warrior boats with a plastic wedge thing, real technical term that, that is mounted on the transom where the engine bolts on.
Now my thoughts are that may be if this is not solid you may be getting some vibration from this.
I don't have one of those "techy" things on my Warrior so I don't seem to suffer from this problem.
Sorry it is not that helpful
Coddy