I recently moved into a new custom home and began noticing a smell from the septic system. The smell is not that of raw sewage, but rather that of the system. I've shined a light down the drain to see if the shower drain has a p-trap, I was not able to see a visible waterline in the drain. I'm sure it does however the foundation was already pored when we bought the home. Any suggestions?

Pour water down the drain to establish that there is a trap and its filled. If this is brand new construction the trap may have dried out from non-use.