It's been bugging me for months, I lock my games @ 150fps with Rivatuner, and vsync off, 144hz. Even just sitting still on track I'm watching my FPS, every 5 seconds or so, it would drop from 150 to around 100 then instantly back to 150, this would cause a stutter every time and was horrid, even Vsync'ing at 144hz with a 3 frame buffer didn't solve it. I found out that when the game was open and maximised Windows 10 Anti Malware was scanning it, using CPU and HDD, as soon as i minimized the game, AntiMalware service would suddenly stop. Very strange. Anyway I disabled it via registry and now the game has been stutter free for days and it's AWESOME! Press Windows Key + R to open the Run Dialog Box. In the Run Dialog Box, type regedit and click OK to open the Registry Editor. In the navigation pane on the left, double click the folders to navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender. If you find a registry entry named DisableAntiSpyware, double click it and set its value data to 1. 4b. If you do not see a registry entry named DisableAntiSpyware, right click in the main Registry Editor pane and select New > DWORD (32 bit) Value. 4c. Name this new registry entry DisableAntiSpyware. Double click it and set its value data to 1. 5. Restart your PC Hope this helps some people suffering as I was.