Smelly Washing from my piece of equipment!? My Zanussi machine is not exactly foreign but works perfectly. However a...

My Zanussi machine is not exactly foreign but works perfectly. However a few years ago wash started to come out smelling vaguely approaching - to be frank - vomit! Then it stopped happening. But for the final year it's been arranged again. It doesn't seem to concern what powder/liquid I use, if I use conditioner or not, take the wash out as soon as it's done, dry it indoors or out! I cannot understand why this should crop up. I clean the drawer etc regularly. It's driving me insane. Has anyone else have this problem? I really need an answer on this one guys!
Does this come rotten?
Answers:    You enjoy a sewage back flow. Your drainage is not passable. Thus causing a vacuum of sewage and gas. Have this inspected ASAP.