That's a sign of possible infection, yes. Is Norton set to use maximum heuristics, and to scan all files with no exceptions? I did a quick Google search for "virus opens cd-rom tray" and some of the different viruses that can do that have these risk factors: no firewall protection, file-sharing software, MSN Messenger, and unpatched Windows systems.
So you might hit Windows Update a few times until your system is fully patched-up, install ZoneAlarm basic firewall (free), update MSN Messenger or other IM programs you might use, and double-check your Norton setup with a fine-toothed comb to make sure it's playing hardball.