Can't find source of mold smell

Hey folks,

About a month ago we started smelling a very intense mold smell that was isolated to one room of the house (my daughter's bedroom). We had recently had the house power-washed and painted, and I thought perhaps one of the faucets we turned on had a little leak, or maybe something they sprayed got in somewhere. So I started taking the usual steps to try and find the source.

- We emptied out her room of all items and the smell persisted.
- I had an inspector come out and he could find no damp places, and the drywall is entirely solid, no soft spots.
- I went to the attic and checked around the ceiling but found nothing (and no smell).
- I went to the basement and sniffed around the edge of the slab, but nothing. No dampness at all either.
- We had the vents cleaned, deodorized and sealed, but the smell was unaffected.
- I checked the fascia outside. Nothing.
- I removed the faceplates from the outlets and light switches and sniffed. Only one (on an external wall) smelled strongly of mold. It was directly under a window, so I removed all the drywall below that window. Nothing. The insulation is fine, there's no mold on the drywall, nothing there. Sniffing around the edges doesn't point me towards anything that smells like mold either.

There are a couple other weird features to this mold smell as well. Randomly, throughout the day, the smell will completely disappear. For example, every morning the smell vanishes for a while. Over the night it becomes really, really intense. Over the rest of the day it's up and down, but it's always only this one room.

I'm out of ideas.