If the speaker cone is made of paper, and you got it wet, while washing the car with the doors off, this might cause the problem. The night dew may have got the cones wet too, with the doors off. A closed vehicle would protect them, but not open doors, especially if the vehicle is outside at night with the doors off. Once you get paper cone speakers wet, they are toast. They don't last long regardless anyway. It sounds to me like you have paper cone speakers.