Ever since I upgraded to OS 10.2.3, my Sonnet ATA/66 card has not worked right. I have two hard drives connected to it, both in a "master" configuration on the two different controllers on the card. OS X runs on a hard drive on the original system controller. I have had these two drives on the card for about two years now and they have run fine.
Once the OS 10.2.3 udpate finished installing, and before I had restarted the computer, the 30 GB IBM Deckstar drive dissapeared from the desktop and started "chunking" (making a noise like it was scanning back and forth quickly). It was loud enough that I could hear it even though the G3 tower lives in a cabinet. I restarted several times, but could not get it to mount or stop making the horrible noise. The other drive on the card (the original IBM 6 GB drive that came with the G3 B&W) mounted fine.
So, I disconnted the power and ATA ribbon from the 30 GB drive, figuring something happened during installation that screwed it up. When I restarted, the 6GB drive, which had been fine for several days while the 30 GB drive was misbehaving, started exhibiting the exact same behavior! I have since disconnected them both and have a new ATA/133 card on order.