Help with removing an odd smell in room

[AvaH]

How Does One Handle "Hypersensitive" aka Picky Princess Guests?

I probably shouldn’t be so annoyed/uptight over this issue but I am. My listing is a 72 year old home. It is built with recycled redwood timbers from a train station that was old when it was torn down and the walls are plaster instead of drywall because of the time period the house was built, 1946. It has no dampness or mold issues, we have checked numerous times and stay of top of it. It does have a faint musty smell when it is closed up for a day or two. The smell dissipates quickly…

This post of mine had a great deal of advice re: smells, even though that wasn’t what I was originally inquiring about LOL

Update on that situation, the smell has been eliminated. We got a new air cleaner without the ionizer option. We also used a no scent air odor eliminating inside the main body of the antique piano and no more smell. We think the felt hammers were holding odors.