music hall mmf 2 platter out of balance?

Over the past month or so, I have noticed the platter on my Music Hall MMF 2 going out of balance frequently. Maybe that's not the right term? what happens is that when i start up the turntable, it will rotate and start to rumble a little. Sometimes i can make it stop by shutting the motor off and turning back on, sometimes it works after one try, sometimes it takes many. Is this a matter of greasing the bearing shaft or somethign like that? I'm a bit of a novice with turntables so it is probably something obvious.

thanks.