Put the stopper in the G/D and see if it will go away.
Many disposals that are on their way out will smell bad because they won't dispose of all the food. Some of it gets stuck in nooks and crannies as rust forms and tolerances become enlarged and begins to rot.
Sometimes the flange that holds the G/D will allow water under the flange and it can stink.
Could be a trap not pitched right holding water in the drain line leading from the trap and forming a layer of goop that will cause the trap water to smell.
Try pouring 1 cup of bleach in each trap B4 bed and let it sit all night. Run the water in the morning and see if the smell is gone.