little help with a chevy metro? haha

I've got a 98 metro I drive sometimes to save money lol and it recently started making a bad vibration noise when going around 55mph but not all the time, it starts and stops randomly I thought it may be a wheel bearing but I jacked it up and all of the wheels are pretty tight, the front moves a little bit but I think its just from the steering because the rods connecting the wheel moves too, but very little, anyway can anyone tell me what else could cause this vibration? its getting worse everytime I drive it and I'm afraid I'm gonna be on the side of the road soon.