If you feel it is from sort of organic matter, you need an eznyme based
cleaner/deodoriser to get rid of it. Prochem do one as do ValetPro, the
VP one is called Enzyme Odour Eater but not sure what the Prochem is
called; call them to find out and then you can simply collect a small
container from a local janitorial supplier :)
You mix it up with warm water, spray it on generously, and then you
would spray some on a towel of some sort dampened with water and place
it over the offending area so it remains damp for a good few hours.
--
David