Hi... the rear part of my exhaust just fell off.... not sure if it's a 2nd muffler or a resonator or what... but it's south of the real muffler at the rear doors. It is stamped with a GM part number 8MX-BOX00185-02... the first "O" could be a zero, hard to tell. The first 8 is definitely different from the B in the 4th position. Tried all the combinations though and can't find a reference for what part this is. Any idea? Car sounds fine without it though, so I don't THINK it's that important.