If you accidentally leave half a sandwich under your bed for a few days, cover your nose while you sleep because it will probably become quite noisome. This is a fancy way of saying that it will stink.
Despite that first syllable, this adjective doesn’t have root origins in the word noise, but is related to the word annoy. Noisome can refer to anything unpleasant or anything that makes you nauseous. However, it is most often used to describe bad smells. So spray some air freshener, open the windows, and clean out under your bed!