Hi there,
if you playback a SMTPE Timecode with I tunes you might have Drop outs or jumps in your Time Code.
This is caused by the sound enhancements from I tunes.
You need to switch them off with the following steps: settings - playback - sound enhancement. The Default from Mac is on, so you need to switch them off. The same on I tunes on Windows Computers, but on Windows I think the default is off.
For the german user you need to go these steps: Einstellungen - Wiedergabe - Klanverbesserung