I have a 2006 CTS. Today I wanted to try a new DVD out and removed the map disk from my Navigation unit. The new DVD would not load and when I install the map disc back in it will not load. It just pulls in and then a noisy vibration sound occurs for a few seconds and then stops. Disc is not loaded. Waiting with the disk still in, It will again start the noisy vibration noise and then stop. I eject disk. no apparent damage but can't get navigation to work again. Any ideas as to cause of problem.