I had this problem as well with a Western Digital drive in the caddy when used in place of the DVD drive, the solution I found online was to use a Seagate drive (Seagate's still have jumper pins) and install a jumper that would lock the drive to SATA I speeds. Once I did this my drive performance became consistent. Just as an FYI, the Seagate exhibited the same performance problems as the WD did when I tried to use it without the jumper.