zzzzz most often a buildup of sludge composed of detergent or powder, fabsoft, and grease
This is especially copmmon if you do lots of cool washes or are overgenerous with the detergent.
Do a MAX HOT wash with old cotton towels (preferably white) and NO POWDER. See if it foams up. If so, the very hot water is washing away the sludge.
Also take out the powder/dertergent drawer, it will probbaly have sludge and black mould in it. Scrub it with a nylon brush and hot water. Also clean the slot that the drawer slides into. kitchen spray with bleach and a nylon washing-up brush.
Scrub round the rubber door-seal especially the grooves and channels that you can get your finger in
Another common cause is rotting fluff and socks in the pump filter. Take the filter out and clean it. The instructions are in that booklet you received when you bought the machine and haven't looked at since.
There is a much less common problem with incorrect plumbing of the waste pipe allowing dirty water from the sink drain to get into the washer, but you willl notice it slowly filling up with dirty water and tea leaves when you pull the plug out.