I found out that if i quit the G-Sync mode (between 90-144Hz) i get the spikes.
So i tested some things like cap the FPS ingame via Nvidia control Panel, activated V-Sync (just a test), reduced the grafic settings and nothing worked..
It doesnt matter how high my FPS are (AVG on 200+) but the spike drops it out of the G-Sync mode.
Some Ideas guys?
edit: *obviously i tested deactivating Gsync mode = no change