Finally, the OS X has been removed from MSI Wind U100, and completely replaced by Debian (testing).
Whenever the computer is idle, the hdd makes this weird clicking noise. To stop it, we can use hdparm to turn it off.
kenno@tora:~$ sudo hdparm -B 254 /dev/sda
setting Advanced Power Management level to 0xfe (254)
APM_level = 254
Source: MSI Wind – Gentoo Linux Wiki