The Featherweights seem to be particularly prone to musty smells, but I have had similar with cardboard accessory boxes and a book once. It actually took over two almost three years before it was gone. It quickly got better and within acceptable, but completely free took a very long time. I wiped them with a damp cloth, had them in the sun for a few ours two days in a row, but sun can be harsh too so I limited the exposure time. The rest aired off on a clean book shelf in a dry heated room. Next time it happens I will implement tricks like activated charcoal, bicarbonate or coffe grinds.