I just bought a 2010 V6 Outback. At 700 miles, it started to have a vibration at 40-50mph, now it does it at 20-30mph. It sounds and feels like you are driving over rumble strips or a cattle crossing guard. Sometimes it is soft, sometimes it's enough to vibrate the entire car. Right now it is back at the dealer. When it is making this sound and you toss into N, it stops immediately. Has anybody else had this happen?