yeah mine didn't fit properly either, ASG ended up adding extra metal to make it fit, so when i take it back ill see what they say... The knocking is annoying like hell, can't stand it anymore. I think it might be the dump pipe not matching up to the hanger. I don't know if ASG cut the dump so it can actually hook onto the hanger, if they didn't than that is most likely the problem because the dump was about 2cm lower than the hanger.