If you weren't have any radio interference problems. Your motor could have been a little dirty and corroded or even a loose wire could be a culprit. I would open it up and put a light oil on the motor bearings and grease the stuffing tube. As I am not familiar with that particular boat I can't help by telling you how to do it. Other than that if the problem goes away with a little more use then great. If not then it might be time to put in a new motor and prop shaft. good luck
mike