My O2 sensor was touching my frame with my Zard full system. It broke the bung out of the exhaust. Hope it just happend to me but it might be worth checking. I had to cut 1/4 inch off the 3 int 1 section of header to make it fit after it had been welded back. It wasn't in the exact same place after being fixed. It was close when I installed it new but vibration must have done it in.