I have the Friedrich Motorsport Catback with stiffer hangers.
Do you plan on keeping the car? Then put it on the lift. Everywhere you think it could hit the underbody, take a wrench or something and just hit that aluminum thingy and bend it inwards a bit (yes, that sounds very cheap and idiotic but it worked wonders for me, it won't be able to hit that spot anymore no matter the movement). Oversize catbacks here in Germany and switzerland will usually hit the underbody, even with different hangers and all sorts of trying to fix it.
I'll Keep my car until it gives up so that was the best solution for me.