If it’s a strange sour smell, it may me created by bacteria that love a bit of humidity. The only way to get rid of the smell is to kill the bacteria once and for all. You can do it either by 1) using bleach (soak for 10-20 minutes in chlorine solution (the only occasion I ever use it), 2) airing the smelly items in sunshine so the UV rays can do the job. To avoid it in the future, be sure to dry them in plenty of air, and as quickly as possible. Freezing kills dust mites, but not these miserable creatures. Good luck! Kay
If it is coming from the wood then maybe washing it down with a bleach might work. I would use bleach let it sit a few minutes then rinse it throughly. Then use a bleach solution and let it dry. Then rinse it off. Let it dry throughly and then paint the wood with mildew resitant paint. Don’t forget to do the door as well as all the walls and cupboards. I would also do the suggestion for cleaning the sheets stated in the previous entry. Both combined should remove the odor.
My stepmom has this same problem. I would recommend washing the linens with 2 cups of white vinegar in the washing tub, every time. Also, keep a cup of baking soda in the closet to absorb any odors there. Good luck! ;)