Yep, mine is the same. I built my new rig yesterday with the ROG GTx1070 Strix OC and spent today gaming... (well, spending more time looking in the case than at the screens lol)
Playing fallout 4 was silent until the gpu started working harder. The 2 outside fans spun up first, then i launched a ton of mini nukes for a while and sure enough the 3rd (central fan) spun up.
Seems normal
