HAHA very nice metaphor actuallyMine is a 99 and it does it a little... not very much, its still on track but you can grease it if its really bothering you
Its doing it bc as it is going down the track there isn't very much lubrication so its not sliding smoothly down the track. Kinda like if you take ur hands and drag them across a glass table and ur hand kinda bounces a little bc its gripping to much. (prob a crappy example lol)
he is also right it might not be on track right or the motor might be calling it quitsit may need some grease, but i would look to see that its still on the proper track. could also be the motor failing