Question on CDROM access

Hi, I am running Ubuntu 11.10 and my CDROM drive's LED keeps blinking. I want to know which process is accessing CDROM for no reasons. There is no media in the drive, I believe OS seems to access it for media change events, but I am more interested in which process or deamon is actually doing it. I tried the followings and nothing gave anything: 'lsof | grep -in 'cdrom' 'lsof | grep -in 'sr0' 'lsof | grep -in 'sg0' What tools could I use to track down the process, which is accessing my CD drive? Thanks in advance. Asahlot