I've been experiencing a rotten-egg / sewage smell in my home. It occurs mainly in the summertime but it is not constant. The smell seems to be stirred up by two simultaneous events: (1) running water down the kitchen sink, and (2) the central air-conditioning kicking on. It is especially bad when I arrive home from work on a hot day and flip the A/C thermostat from 78 to 75 degrees, and run water down the kitchen sink. If I do not run water down the kitchen sink, the smell does not appear. After a few on/off cycles of the A/C, the smell dissipates. Any ideas on what the problem could be? As far as I can tell the A/C and plumbing systems are working fine. No drain line other than the kitchen sink appears to stir up the smell.