Can you tell us a bit more about how they smell and your washing routine? Are you doing a cold rinse before a hot wash with powder followed by a further cold rinse? If you go straight into a hot wash you can 'set' smells into your nappies. And as previous poster said, if you have hard water you might need to use more powder to get your nappies clean. If they have a farmyard smell coming out of the machine then they are simply not getting clean enough in which case you need to wash with more powder. Or do they smell of wee/have an amonia smell as sooon as LO wees? If it's the latter, they probably need a strip wash to get rid of detergent build up.
Synthetic materials also tend to hang on to smells more than natural materials whch could be why it's your fluffles and PUL wraps that are the problem.
Useful chart on getting to the bottom of smelly nappies (sorry for the pun
) here: viewtopic.php?f=19&t=106234&p=1111151&hilit=lingering#p1111151