The Outback started vibrating indicating an out of balance tire. I was due for a rotate and balance so I took it into my tire man today. He checked the right front (which is where I thought it was coming from) and it was right on. Took off the right read and told me he had found the problem. Seems that mud had settled in the wheel when parked and solidified. He put it on the balancer and it was 4 oz off. Same on the left rear but only 2 oz. off. Cleaned them both out and they checked out fine. Got back on the road my old smooth ride was back. Like I said, never heard of this but as I live on a gravel road I am going to have to check this more often.