a few weeks ago i started to notice a vibration coming from my 2000 xj while i was sitting at red lights. i was not sure what it was so i quick shut it down and started it again. i noticed that as i moved the vehicle into park the vibration stopped. so i drove till i got to the next red light and it started vibrating again. i put it in nuetral and the vibration stopped. i am assuming it is probably the drive shaft and the yoke before the rear diff. is there anything i should look for on either to try and find the vibration. it is kinda a hard vibration and i dont think it is a good thing. i did do the pinion oil seal about two months ago, might i have done something wrong while putting in the new seal?