2000 SE 2.5 .got a rattle at around 2200 to 2500 RPMS. First thought it was the Cat. replaced Cat and exhaust pipe. still have rattle. got my rubber hammer and started whacking things to find the rattle. decided that it now must be the muffler, probably OEM. still when I would whack it, it did not exactly match the rattle, but close. I also have this little miss. this happens mostly when we have the A/C on and I let the rpms drop under 2500. yesterday, CLE came on. got the code and it said O2 bank one. cleared the code and it has not come back on. Big question, could a clogged muffler cause an O2 code? I am going to replace the muffler next week. We installed the O2's when we replaced the engine. they are not very old, I know they can fail, but could the muffler cause a false reading?