JP remove the acess cover over these ejectors and check the seal around this access panel.
You may also find it advisable to unplug these pumps pour some Clorox (bleach) into a near by drain connecting to this sump.
Let this stand about 1 hour then plug in the pumps and this should kill all the bacteria that could be causing the smell.
Try using caulking around the pump covers and have the main vent checked for a possible blockage.