Audio descending into static in Sonar 8.5...

I'm having a really frustrating problem with Sonar 8.5. I am scoring a film, and ten seconds into loading up the project, the audio output descends into static. It almost sounds like I need to up the buffer size - but the computer itself isn't doing any work. The project consists of MIDI files that are farmed out via my Fireface 400 to another computer running Gigastudio. The only "work" my Sonar computer is doing is receiving the audio from Gigastudio, and there is also one instance of Dimension Pro running. If I mix down the audio whilst I have the static problem, the resulting WAV file is fine. However, upon loading Sonar again, I get about ten seconds of perfect audio before the problem occurs again. The first time this happens, I ported all the midi files over into a new project - and had no issues for about 3 hours. Then, it happened again. Loading previous projects once the static has taken over my audio also results in the same problem - but if I load these projects prior to loading the film I am working on, there is no issue - until I load up the problem project. The film was sent to me as an MP4, with the audio as an AIFF. I've never had this problem before and I am tearing my hair out to deal with it!!! Any suggestions? Any help would be MUCH appreciated! PC (A8N SLi Deluxe motherboard), Win XP, 2 gigs RAM, Fireface 400...

I'm sending the midi files out to the second computer via the MIDI1 port of the Fireface 400, and receiving the audio back via ADAT. I always work this way - distributing the load allows me to work seriously big projects on two slightly older machines! The film is loaded into the project (standard "import"), and the issue seems to arise about ten seconds after loading the project. I have just converted the film to AVI, and the audio to MP3, and started the project anew with these. Hopefully that will sort the problem. It is a pain though, as I find Sonar fairly sluggish with scrubbing through AVIs - it tends to be much faster with MP4s. The joys of technology, eh?