I have a similar problem with a 3.0 rom'd A4000. I suspect a problem with the ide timing. I have a slim-line 2Gb Seagate drive and a 4x ide cd rom. The cd rom works great but I keep getting random freezes when trying to access the harddrive. I was thinking the 3.1 roms would have bug fixes to make the internal ide controller more tolerant perhaps. You might try using it with an original spec'd 120MB Seagate drive (these were the drives the 4000 originally shipped with).
