Six beeps and then the spinning beach ball

Using Final Cut Pro 5.1
My Quad G5 (2.5 gigs of RAM, OSX 10.4.6, QT version 7.0.4, with MediaVault (2.5 TB SATA, Mediavault firmware revision 017b) and Atto UL4D has worked well for two months until two weeks ago. A co-worker was using the edit desk that I always use and he experienced the six beeps from the MediaVault and then everything froze with the beachball spinning. I was out of town, and he phoned Ciprico support. He was told that if he had on the timeline any audio without video above it or any extraneous piece of video or audio further down the timeline with a gap of nothing between, this could cause the beeps. He cleaned up these odds and ends and finished the project okay.
I'm doing basic SD editing with one layer of SD video captured from BetaSP tape through my BlackMagic Extreme card and a closed caption video layer -- stuff that I do with no glitches every week, and am pretty much shut down because the beeps occur and the whole thing stalls at random places within the first couple of minutes of playback of a 30 minute program.
I have selected Unlimited RT and Safe RT with the same basic results.
The video footage that is being used when this happens is varied, uploaded from BetaSP tape or captured NOW from the same tape deck. No dropped frames happened during any of these captures.
I ran the Blackmagic Disk Test and the basic bold numbers at the top show 169.7 read and 282.4 write.
I'd be grateful for any and all help.
I'll check my e-mail and this forum, but my cell number is 251-510-7004.
Thanks to all.
Greg Golden