Rotted Food

• A bad smell coming from the bottom of your refrigerator is often caused by rotten food in the fridge. Always check the inside of the fridge itself for spoiled foods, leaks and mold if you start to smell something foul. Pull out any drawers and check underneath them to ensure that food didn't fall between them and spoil. Clean out the fridge with a light bleach solution and then put a fresh box of opened baking soda inside the unit to help remove food-related odors.
  
  

Food or Beverage Leaks

• Food and drink spills and leaks aren't only a concern in the fridge itself. Unplug the fridge and remove the front access panel at the bottom if the smell persists after cleaning the fridge. Look for any spilled liquids or food that has rolled under the fridge that could be causing the smell and clean it up. Pull the fridge right out and clean the area underneath it as well. Because food and drink is constantly coming in and out of the fridge, it is easy for something to get spilled or dropped and missed once it ends up under the fridge.
  
  

Mold

• The area underneath a refrigerator is an ideal place for mold to grow. If moisture gets into any of the crevices under the fridge it can result in mold, which often smells quite foul. The moisture could accumulate from spills and leaks inside the fridge, but could also be caused by a faulty fridge component. Fridges with an ice maker sometimes have problems that result in moisture accumulating under the unit, for instance. The drip pan at the rear may also be hiding some bad smelling molds.
  
  

Clogged Drain

• Fridges that defrost automatically have a drain system that clears away moisture that appears when the fridge is thawed. That moisture normally evaporates, but sometimes the drain gets plugged. When this happens, the water builds up and can start to smell. In many fridges, the drain releases the water to a drain pan that is underneath the fridge itself, so a clogged drain is another potential source of odor from that section of the fridge.