Before this potentially becomes a larger problem, I'd like to diagnose it now, if possible. 2000 F150, 5.4, 4X4, 54,000 miles. Sometimes, on startup, there is an obvious vibration coming from the engine which driver and passenger can feel in their seats. I said "sometimes", because it does not happen all the time. When it does occur, it's on cold startup. Not when starting after it's warmed up. It goes away approx. 5-10 seconds after startup if you just sit there and let it idle. Sometimes when I feel the vibration, I immediately put it in gear and back out of the driveway to see if the vibration will continue, but it stops when you go into gear. I don't know how better to explain this problem, but it's an obvious vibration that is not normal. Also, engine sounds fine when the vibration occurs. Once, upon startup, the vibration was there, I popped the hood, opened the door and tried to race around to the front of the truck and look into the engine compartment, but could not visually identify any problems. Engine seemed to be idleing normally. I mean, no "out of the ordinary" engine movement, like broken motor mount. But, I'm not ruling anything out. Any help would be appreciated. Knock on wood, I've had zero problems with my truck since I bought it new in 2000. Hopefully it's not time for stuff to go wrong.