Foul smell in water - not sulfur

[bhitte]

We have an odor in our water - not the sulfur odor (we are familiar with this and occasionally get it when we do lots of laundry & the aerator can't keep up), but more like something rotting or a dead animal......
We moved into the home about 10 months ago - it was previously a model home & sat virtually unused for two years. We have an artesian well and have been told with a well of this depth that the smell is not coming from the water source.
The smell began in November; we had the system shocked with chlorine and the smell was gone until a few days ago.
The smell comes from both hot and cold faucets.
I've been told by the health dept that this is unusual for artesian well water and sounds as if maybe something has crawled into the aerator, or maybe we need to clean the bladder tank. Before we get to an expense like cleaning/replacing the tank, is it possible something could have crawled into the aerator and is somewhere we can't see it? Because we've cleaned the aerator several times since moving in and never seen any signs of "critters". And the water pressure is fine, no sign of any blockage.
One more thing - we had a water softener installed in April; could this be a source of bacteria or causing the smell?
Thanks for any input! (And in the meantime, we're going to bottled water for drinking.)

[Vey]

Filters? If you have any filters, you might try changing them.