In my house for 17 years and never had a leak in my basement. Noticed 3-4 cinderblocks in my basement leaking through the cement seam area and the seeping pools about 1/2 cup of water per day consistently. I have dug up the outside of the house to the slab level and the dirt is relatively dry. I have drilled holes in the 3 cinderblocks that are leaking and I can see standing water in the base of the block and the outside facing wall of the block is wet. Seepage is still only from the seem, not out of the holes and I have no water piping above or outside the house leaking into the upper blocks. Today I drilled a 3rd hole in an area 2 cinder blocks away and the inside of that block is wet as well. Mysteriously the active leak stopped. No idea where the water in the blocks is coming from and if from outside why no wet soil. Also air is actively blowing from the holes in the blocks-Major frustration on an answer.

Relatively dry is just that - 1/2 cup of water in that much soil is nothing compared to what is really there, even though it may appear dry. The concrete industry says that changes happen all through the years, not to mention any waterproofing that may have deteriorated. It is spring, there is more water in most of the US now, so this is to be expected.

In addition, if you have humidity in a heated basement, it works it's way into the walls just like any wall. Sort of paradoxically, if you run a dehumidifier, that will draw moisture in from outside. I read a university study of concrete basements saying that dehumidifiers are worse than useless.

All this assumes that you really don't have water coming down the wood walls from eaves (snow melt, ice dams) or from water supply/heating above.