redforesters

My 2001 Forester makes a loud sound that seems to correspond directly with the moving of the car. No sound is present when the car isn't moving. At low speeds, the sound has a lower pitch and a slow frequency. As speed increases, the pitch and frequency increase. The noise seems to be coming from the rear of the vehicle. The noise has become louder at all speeds in the past week, and it is very loud now. Any thoughts on what the problem could be?

I have a 2001 Forester L, about 74,000 miles. Last summer on a trip to Colorado and driving in temps approaching 100 degrees, my Forester temp gauge was repeatedly going to the three-quarter mark, at which time the A/C would stop blowing cool air. This would happen when I was driving more than 70 mph. Less than 70 mph, no problem with temp gauge or A/C. During the trip, I brought it in to have the cooling system examined. They said everything looked fine. After returning home, I didn't have any problems, but I was only driving around town and the outside temps never were extreme. No problems of any kind in the fall, winter and spring. Today, with the temps more than 90, I took the Forester on the highway, with four people in the car and the A/C going. After about 15 minutes of 60 mph driving, the temp gauge went to the top, just below the red zone, and the A/C stopped blowing cool air. I turned off the A/C and drove home immediately. I checked the coolant level -- no problem. So, any advice on what the problem might be?