Shelly,..
Kinda sounds like something my washer does every once in a while.
Mine's a top loader so it's a little easier to get a look at what's going on. If your problem is like mine, the "shut off" valve isn't closing completely and water is dripping in.
It happens maybe once every 20 or 30 loads so even though I've known what the problem is, I haven't bothered fixing it.
Of course, like I said, mine's a top loader so it would take a long time to fill the tank and start leaking.
IHMO, I would get a repair guy out to check it out. If it is just a valve that's getting stuck, I can't see it being super $$$. And depending on where your washer is located, you don't want to get water damage.