weird vibration that changes with speed and turns..?

id like to get some opinions on this before i get it checked out. when im idling theres nothing. as soon as i start driving the vibrating starts. the faster i go the higher pitched it is and it gets slightly louder. if i turn left, it goes away completely. if i turn right, it gets worse. :confused: rear alignment maybe? i really have no idea. also its louder in the back seat than in the front. if you have any ideas bring em on. thanks.