My machine really started to stink when I only used non-bio liquid when my daughter was younger...I googled it (as with everything) and apparently there are no enzymes in the non bio to kill any bacteria when washing at cooler temps.
It didn't take long after switching detergent for the problem to go away...it's a horrible smell, esp when your clothes warm up on you, bleh...at least i was getting a double seat to myself on the bus regularly! x