corrupted file / clicking noise when attempting playback?

sometimes my ardour files get corrupted and the only sound i get out of them is a “click” everytime i press play/stop or i change a connection in jack!

this is on a macbook running osx10.4.9 w/ jackosx and ardour 0.99.3 (although the problem does not correct itself after i downloaded version 2)

more info:

apparently, its only some of the tracks that are causing this problem? for instance, one of my drum tracks, when i connect it to the master in, it kills the output, but the other drum track i have doesnt…

what, if any, plugins are you using?