i have a 900 zxi. took it out today and when i was near full throttle i felt it vibrate and heard somethin like rattling and it slowd way down.... did it to me twice... so i ran it half throttle all the way to the dock and it ran fine... starts up fine and sounds fine... afraid to get on it again.. yesterday i ran into a sand bar and suckd up alot of sand could this of cause a problem. im new at jet skis so please any ideas...