Last week when I had the wheels off and was putting the steelies back on my car, I had noticed one of my exhaust hangers was broke. It was causing a very anoying sqeak for the past month or so. The only way I saw it was by having the wheels off, not sure if it is your problem or not, but my exhaust is only 2yrs old and it was still broke. Good luck!
1997 Mercury Grand Marquis LS/SS *Goodbye old friend*
2003 Mercury Grand Marquis GS