I have been using Premiere 6.5 on Mac for a while now and I have a very frustrating and annoying problem. Occasionally I get no sound from either the monitor or timeline when playing back clips? If I drag the meter along the clip I can hear the sound but not on playback. The problem is sometimes sorted by simply shutting down the computer and restarting, but it is a problem that re-occurs.

Any help will be greatly appreciated.