What sensors did you have replaced ? I recently went to the stealership and the told me that I needed converters immediately following a repair on my rear main seal. I had never had any check engine light issues previously. I scanned it myself and found codes for BOTH LS O2s. After testing,they seemed to be operating properly. So I happened to start the car when it was REALLY quiet in my garage and heard a slight hiss noise coming from the LH side. Upon further inspection, I found a hairline crack going half way around the cat at the bottom of the cylinder shape of the cat where it tapers to the base. We removed the cat and welded it closed. No noise and no check eng light / O2 codes. Looks like it might be caused by the condenser drain. Just something to check.