%USERPROFILE%\Saved Games\Eidos\Mini Ninjas
It seems certain motherboards/chipsets combinations can cause the game to stutter every second or two, depending also on the connected HID Devices (keyboards, mouse etc.). There is no known fix other than changing motherboard and chipset or trying to unplug or disable the affected hardware.
Install OpenAL and restart the game.
Ambient Occlusion compatibility
Ambient Occlusion usage
Ambient Occlusion setting