I'm going crazy. I have had a sulphur/sewer smell going through A/C vents for 6 weeks. As soon as I smell it, I turn air off for a while ... then it's OK. IT ONLY HAPPENS 1 TIME A DAY. I've had A/C people, plumbers. No one can find anything. The last 4 days we're figuring when I load/unload dishwasher, that's when smell happens. No smell in sink or dishwasher. What could cause this???