Hm, I sometimes (rarely) see something like that on my 60GB unit under 2.0b11. There are no error messages on serial (I am pretty sure I looked quickly enough), but 'W' usually appears by the drive icon. It looks as if one of the drives sometimes fails to spin up as quickly as it should.

When it arrived, the unit exibited classical faulty drive cable problems (blocking in the middle of boot etc), but they have gone away, so I didn't find courage yet to open it and install the replacement cable David sent me.