ThinkPad T520 hdd led always on

[luca9903]

Hi, I recently bought a T520 with quad core i7 and nvidia graphic. When I turn it on the hdd led blink normally but after few minutes it stays on (the light is on and it doesn't blink) while the disk usage is low or 0% (I have a intel msata 310 ssd and the thinkpad mechanic disk inside). I noticed that if I push the optical drive button it starts blinking and works normally. If I remove it from ultrabay the led works normally. The BIOS is updated and i Tried with another ODD form a T520 with the working led.

What Can I do? Why the led is always on?

Thanks in advance, Best Regards.