I wonder if the drives are being run on the edge of their temperature limits. Attics temperatures can vary quite a bit, depending on the arrangement.
In the past I had a dedicated HD control board go intermittent and it made it look like the HDs were failing, but that was back in the DOS days.
Toshiba made some really amazing TVs in their time, but my experience with their computers and parts was disappointing.
EDITED: 1 Feb 2016 19:55 by HARRYN