New PC - why is the HDD LED flashing when idle?

[FunkyT]

I've just knocked up a good entry level machine:

A64 3000+
MSI K9N4 Ultra-F nForce 500 Ultra
Kingston 2 x 512MB DDR2 PC4200
Seagate SATA-II 80GB 8MB cache
MSI X1300 256MB PCI-E video
Enermax 470w Noisetaker

When idle the HDD LED seems to be flashing intermittently (more often that I'd expect).

The only software I've installed is XP Home SP2b and the motherboard drivers.

Any ideas please?

 

[FunkyT]

I'd like to know what that means as well