[arucano]

If you have a sun roof, it is likely a plugged drain from the roof. You can open the sunroof and use a "weed wacker" line to gently clear the drain. Be careful about using air pressure to blow it out, since you can blow off the rubber hose going from the sunroof to the drain point. Check under the car for drains and clean them out. (I don't have a sunroof on the M6 so I cant go check the exact drain point below the car)
Besides that, it can be the drain from the AC evaporator that is plugged.