No Disk in Drive Message when Idle

I just recently built a new PC and installed my Norton Internet Security 2009 program.  Tonight I discovered when the system sits idle, I get a message indicating there is no disk in my CDROM drive.  I canceled the message and the system left idle mode.  After idle long enough, the message reappeared.  I assume I need to exclude my removable media drives from being scanned.  Is this correct?  I don't remember needing to do this with my previous install.