[mrcaptainbob]

Could be a clogged stink pipe. You mention the smell occuring at two points.....one was after a haevy rainfall, the other is in relatively late morning, after showers, sinks and toilets. Seems to happen after a large intake into the system. Two problems, I think: 1st (easy) is to check/unclog the vent stack(s). The 2nd (difficult) figuring why the septic system is being so affected by haevy rain. THAT is not good! I trust the system was pumped and inspected at point of purchase.