Odd, intermittent FPS drops with low GPU usage

Hi,

I'm running Windows 7 on an Intel i7-2720QM laptop with a GTX 580M graphics card, 8 gigs of RAM and a Samsung 850 SSD drive.

Game performs okay on the lowest settings, at 1080p resolution. However, occasionally (few times a minute) the FPS drops to a crawl for a few seconds. During this time, the GPU usage drops to below 25% (see attached image). CPU usage floats steady at ~65% on all cores. GPU temperature is steady in the low 80's (°C). The GPU is not throttling, core MHz stays steady. No excessive I/O traffic happens. There's no network lag either. The FPS drops don't seem to be tied to what's happening on the screen; I could just as well be in a hectic battle or stare at the empty sky.

Things I've tried:

- Updating all the things

- Every imaginable combination of in-game video settings, including VSYNC, windowed/fullscreen, VRAM limit etc.

- Every individual setting from nVidia Control Panel's 3D settings (I'm not running Experience/Shadowplay)

- Kill all background tasks

- Disable W7 Aero

- Disable Origin overlay

- Roll back drivers from the latest (393.06) to 392.90 (With driver cleaner software)

- Play around with CPU affinity & process priority

- Unpark CPU cores

- Disable RAPID mode (Samsung's SSD feature)

- Sacrifice a lamb

My wit is considerable but I've reached its end. Any ideas?

Thank you.