There is a mildew smell in my guest bathroom. Bathroom is completely tiled no wallpaper no wet towels no fabric of any kind in there. House is on a slab. Can the mildew smell be coming from the sink drain? How can I locate the origen of the order?

It could very well be coming from the sink, especially if it's not used very often. However, if the sink is set in a wooden cabinet, I would check inside. It could also be coming from the shower curtain. Anyway, sorry if I'm of no help.