Hello Ian,
When you insert the disc you'll have heard the whirring of motors and the clatter of mechanical linkages.
That's the disc transport conveying the CD or DVD (whichever you have) into a precise place so that the laser can read it. I must admit that errors here usually result in a "no disc" message and not what you've seen. Having said that I've had to replace the transport on my sat. nav. because it kept ejecting the disc. There was nothing wrong with the electronics. I've also had similar problems with home hi-fi and video equipment.
There's another possibility. You say you have a BMW system so is your installation modified?
Simon