PS4 suddenly shutting down (accompanied by a small whine)

Had my PS4 for about 3 years now and over the past couple of weeks it shuts down randomly after about an hour of use (this happened to my last one as well). When and after it does, it's accompanied by a faint whine.

I took this to be a sign of it overheating and changed the thermal paste & thoroughly dusted the inside and fan today. It ran well for about five hours and, boom, same deal. Is it my hard drive or something?? Or the power supply perhaps?