Your situation sounds really familiar to one we just went through. We also moved into a new house about two years ago and we were having a similar problem. We have carpeting in the room with the problem though so we had to rip it up to find where the problem was coming from. Our floor was cement under the carpet so it couldn't come up from the ground and the wall didn't show any signs of water damage yet the carpet was soaked. Once we ruled out the spilled water we found the problem was that the wall was set uneven with the floor and so during heavy rain the water that puddled outside would seep in through many little cracks to reach the carpet. The theory sounds far fetched but it really can happen. We did just as you were thinking and calked the edge of the wall. Next time there is a storm you might want to sit in there and see where the water starts or put down a towel and see where the most moisture comes from to more accurately target the leak. Hope this helps or is at least reassuring...don't worry you aren't going crazy and there isn't an intruder. :-) Good luck!