Damp or musty
A damp or musty smell is caused when dust in the cyclone has come into contact with water.
It may not be a direct contact with water, for example when vacuuming pet hair that is slightly damp; this moisture will combine with the dust in the cyclone causing the smell.
Additionally the smell may occur if the filter goes back onto the machine wet.
Only the filter and the two washable brush bars from the soft roller cleaner head can be washed. The bin can be cleaned with a damp cloth only, and both must be completely dry before being re-fitted to the machine.