hard drivesometimes takes two seconds to 'kick in'

Hi, I use Windows 7 64 Pro, have a 1 TB Samsung HD103SJ ATA hard drive. I also hooked up two oldered HD from a previous computer. Everything seemed to work fine, but now I notice that once in a while, say if I am watching a movie, the screen will freeze and I can hear a sound as if the HD had been inactive and is now starting up, this takes about two seconds and things continue on. Is this a sign that the HD is failing? Or maybe because of the two HDs I hooked up the power is somehow mismanaged? I am not too computer savvy.

Thanks