I had this problem as well. Firstly, make sure under the system menu change the frame limit to 60. When set to none I encountered this issue. If this does not resolve it, check to make sure you do not have two sound card drivers in device manager. This was an issue for me on my PC as ATI installs an HDMI sound driver with my video card drivers leaving me with two sound card drivers. When I disabled the extra sound card (HDMI) driver, the frame rate stutter was resolved. I realize you have an Nvidia card but its possible Nvidia also installs HDMI sound driver if your card has an HDMI port.

Worth a shot, hope it helps.