ABS Solid, Brake Flashing, Warning Tone?

Every so often when I start the car, the ABS light will remain on. Shortly thereafter, the Brake light with flash and a warning tone will sound. The brakes appear to work just fine. If I turn off the car the let it sit overnight, by the next morning, the warnings are gone. This happened twice now in six months. What could this be? Has anyone else experienced this? (2004 Jetta TDI, 26k miles)

since you're under warranty, have the dealer check it and scan for DTC. What you describe is not normal. It could be something simple like a wheel sensor.