Yes, I am positive. A month ago when I took it to Firestone to get a brake flush they test drove it and thought it might be the U-joint or a pinion bearing, but they said I would have had more vibrations then. Plus the sound came from the rear right wheel area, not the center of the car. I am posting a small update in my next post.
Edit: The update turned out to not be so small after all.. Sorry about that! I have a tendency to include even the smallest details sometimes, which leads to me writing a longer post than planned.