The dust container/FilterBag contains foul-smelling debris.
Vacuum cleaner without FilterBag: Empty the dust container.
Vacuum cleaner with FilterBag: Change the FilterBag.
Tips to prevent unpleasant odors:
Do not vacuum up liquids or any damp dirt. Allow steam-cleaned or shampooed carpets and rugs to dry out completely before vacuuming.
You can also equip your vacuum cleaner with the Active AirClean filter. The active charcoal in the filter neutralizes odors before the air is released to the environment again.