I am experiencing the same problem on a System76 Darter Z35F running Feisty beta installed from the alternate CD. I am attaching information from the machine below.
-- Hard disk I/O randomly freezes when hald is running and optical drive is empty https://launchpad.net/bugs/84603 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs