G5 Second Vid Card interfering with Firewire Audio device


Using a G5 dual-2Ghz with OSX10.3.9. Wanted a third monitor, so installed an ATI Radeon9200 Mac Version card as a second video card. It's a PCI card in the PCI-X slot. My main card is the factory-installed ATI in the AGP slot.

Display works fine, except that when I'm using a Firewire audio device and do anything on the third monitor/2nd card, such as open a folder, move things around, etc, within the display, the audio stream is interrupted and I get a high-pitched whine replacing the audio.

After several seconds, it goes away and the audio returns, but if it's done enough times in a row, it whine stays and I have to reset the audio device. What could account for such interference with a Firewire data stream?

All ATI drivers and ROM are updated. This occurs with any audio software communicating with the card, including iTunes, and the software chugs along happily regardless of the interruption. Just the hardware is freaking out.

Apple, ATI, and the tech folks at MOTU (audio) are drawing a blank. I've tried all three PCI slots, both FW ports, resetting the PMU. The lack of lots of PCI/PCIX extra-vid-card-Mac-options makes me hesitate to rush to get another card.

Any suggestions? Thanks everybody