I have an early 2008 mac pro that has been working fine since i got it just over a year ago. Recently the DVD tray has taken to opening any time the machine is booted. The tray is opened whether there is a CD or DVD in the drive or not. This would just be an annoyance, except that I now need to boot from a CD, but cannot because it gets ejected. When re-starting the machine I get the startup chime, the grey screen, hear the heads on the optical drive moving, then the drive opens and I get the Apple logo followed by a boot from hard drive. Tried holding 'C' key during boot, no difference. I've tried several different copies of both DVD and CD media with identical results. The media works fine in the browser (in the same optical drive - I only have the one) once the machine has started. Hardware configuration hasn't changed in months. Latest software updates installed (OS X 10.5.6). Any one else seeing this, or have any suggestions?