Hopefully the contractor who poured the new concrete floor didn’t bury a clean out.
Since house is 24 years old the internal piping could be partially blocked with years of accumulation of grease and laundry soap deposits along with other bacteria that can cause smells.
The easiest thing to try 1st is water jetting these to a like new condition snaking is strictly good for hard stoppages like roots.
The water jetter will not only scour the pipes clean BUT flush away all the build up at the same time.
You could also get fancy and have a video inspection to double check the cleaning was performed properly.
If this doesn’t do it have a local Master Plumber perform a smoke test to make sure your vents are intact. Good luck