On my 2004 Forester (73,000 miles), when first accelerating from a stop, or when slowing down (not necessarily braking) from
higher speeds, there is a loud rubbing sound coming from the rear. When I first heard it, it seemed as though I was dragging something under the car, but I checked and found nothing hanging down. The sound is not continuous, but periodic, and increases with frequency as I speed up, until it stops completely when I reach approximately 35 mph or so. As long as I am at normal highway speed, I don't hear it. But as soon as I slow down to below a certain speed, it starts again. I can't tell if it is coming from the right or left side. Does anyone know what this may be?

possibly a stuck brake caliper.