You could clean it up and tent it off for six months. At least you'd know if it were an interior or exterior problem.

Post a picture of the corner of the house that shows the roof to foundation.

What rooms are in that corner of the house at each level?

Are there weep holes at the mortar joints where they meet the concrete foundation wall?

Does your spouse snore?

Has the downspout been there since the house was built?

Thank you for your help.

To answer the questions:

1. In that corner of the house there is a bedroom and an unfinished workshop space in the basement.

2. There are weep holes at the bottom of the brick siding. The previous homeowner had caulked them all and we opened them up in November 2021.

3. No snoring. Lol?

4. We are new owners as of Nov. 2021, the gutters and downspouts were completely missing when we took possession. We had them re-installed in November as well. No idea how long they lived without them.

Photos below.

I would suspect the weeps first. Are they just mortarless joints or plastic tubes?

Its possible there is no protection in the cavity and mortar or debris is blocking the weep on the back side of the brick. Its also possible the brick shelf slopes down to the corner a bit and another weep might be needed at the lowest point.

Or mayby there's a very tall dog or a horse in the neighborhood. Or a disgruntled neighbor.

Siding is attached to the face of house sheathing. Its usually wood or simulated wood. Thin brick can be adhered to the sheathing too but its not called sding and modular brick that sits on a brick ledge and has a cavity behind it with weeps at the bottom like yours is called a brick cavity wall.

I did not think about the horse theory.

Thanks, @res2architect for clarifying that it is actually a brick cavity wall.

The weeps are mortarless joints. Perhaps the corner could use another weephole then to allow this moisture out.

Thank you, Mark, for your thoughts. I'll have the gutter system looked at again in detail.

My only other idea was that there could be frost/condensation build up in the wall assembly from air leaks around the floor framing? There is no vapour barrier in the basement space below. However the dampness in the brick is appearing above the basement level.