I found the magnaflow was designed with a flaw with the right hanger post; it doesn't have a bend in it to stay in the rubber grommet. Mine actually slipped out and once I finally got down there I found the problem.

I took mine in and the shop heated up the end and put a bend in it and it seems to be holding well. Some have suggested using zip ties to hold pull the left and right grommet's together and that will also help. I haven't gotten to that point, but it does make sense.