I get this annoying noise whenever I hit play on HD Vid (720p/1080p)
Whatever uses GPU power, it starts with it, games, benchmarks, etc.
I've read it could be a defective capacitor and should ask for replacement (has no longer than one week, and does it from day zero)
I can turn on Prime or some other CPU stress tool, and it will stay silent, but GPU
It's a common problem with many GPUs. What you're hearing is the swan song of an induction coil on your graphics card. Eventually it will probably fail. I've had to replace a GTX 295 after dealing with about a month or so of the squealing.