 If it's horizontal, fix your drainage. It could be collecting water against the outside, breezing and pushing it in. Or if you're just not sure, get an inspection by a structural engineer or a professional home inspector, not, underline not, a contractor. Contractors that inspect foundations often have conflicts of interest. They want to sell you a big expensive repair. They're not qualified as engineers to make the determination. So I would say a structural engineer or a home inspector are the best two pros to go to.