The slot-loading optical drive on a Macbook (2006) running won't accept a disc when inserted--unless it is partially inserted and then slept/waken or the "Disc Burning" section of System Profiler is visited.
Also, when booted or awakened from sleep, the optical drive constantly/repeatedly checks for media for around 20 seconds or so. I know it's normal for every Mac to check for media once at these times so the system knows if there's a disc inserted or not, and I know it makes a sound, but this is unusually long.
The Macbook passes the self-hardware test (even the extended one you get to by pressing D at boot) and the optical drive will play back the media fine once loaded.
The Macbook's software is up to date.
Any ideas besides a PRAM reset?