The other day I was helping a friend with the treatment of his studio. There was a massive ring at 125. As I ran the peak tone around the room and checked it with my SPL it turned out that the door was ringing. Like 18db ringing. We opened the door and to our surprise the Peak at 125 was gone as well as some lower freq peaks. The room went from +/- 18 to +/- 10. This studio was designed by a major designer as well so it explains why the room became so flat once the door was opened. Since the ringing door was into a storage area at the back of the room it was easy to cure with a nice curtain.
Just a thought but did you try running the peak tone/noise to find out the root cause of the ring or where about in the room it is, while moving your speakers to find the best possible position for the speakers?
Disclaimer:I am not an acoustician, but this method has saved me about 6 times or more while helping friends with bad rooms.
