Sometimes when I insert an audio CD I get a dialog that says "You have just inserted an Audio CD. Choose what application to launch." It doesn't show up for every CD… probably something like once for every 5 CD insertions.
Every single time I select "Do Nothing" and ensure that the "Always perform this action" checkbox is checked. I assume the point of the checkbox is to let me make the decision once and for all, but this dialog continues to reappear periodically.