Aquarius WF321 bad smell?

I called out Dynorod when the smell from my washing machine became so bad the whole downstairs of our house stank of drains. There wasn't a problem with the drains so called out Hotpoint (machine still under warranty at that time). The engineer couldn't track down the smell to one place to replaced the entire insides of the machine. This solved the problem for a few months. Now it stinks again and is out of warranty. HELP!!