Its proberbly gotten bunged up somewherelike the drainage pipework and it clogs in there for months and then rots and as a results when your machine is stood, it tends to stink it all out a bit. This might sound a bit harsh, but using something like extra thick harpic toilet cleaner in a empty wash on a 60 degree hot wash with a couple of rinses should clean it through and leave it smelling loverley and fresh, ive done it twice in a machine less than a year old already!
Andy
July 2008