Radio/tape Cd Player problems of the 2004 Volkswagen Jetta

There were problems with the radio starting one year ago. On three occasions the cd would not eject and the radio would not play even though it could be tuned and adjusted. The cd ejected two of the three times when driving fast over a large bump. The third time I had to hit the side of the radio three times before it ejected. On a different occasion the radio turned on without sound and the cd player would not take the cd. After driving the vehicle for 10 minutes, the stereo accepted the cd and it played. Today the cd I put in was being read but no sound was present. When switching to radio, with the cd in, no sound was present for the radio. Only after the cd was removed and the stereo was turned off then on did it have sound. The dealership says in order to replace the stereo they need to see the problem. However, I can't just stop in when it is occurring because other people have appointments. By the time I have the appointment, the stereo is working and in their eyes it is not a problem.