I have the same problem of overheating! Quite and cool Caviar Green "stocazzo" as we say in Italy!!
Anyway I created an external fan converting a normal case fan into a usb fun. You can find several HOWTOs on the net helping you cutting and pasting the wires. It tooks not more than 10 minutes.
But I guess the problem still remains: after two whole weeks of optimal hard drive temperatures of 30-33 °C (instead of 40-50), I received just yesterday by email the NAS event of volume in degraded mode!! I can't believe the hdd is broken, because every time I resync the raid it gives me no problems, I guess is just a problem of the hardware monitor. To assure this thesis, today I stopped the S96wixalarm service. I will manually monitor the raid status checking the /proc/mdstat interface and using the smartctl program.