Two 1080ti and i7-6800k
This is weird... Perhaps sound card casuing frame stuttering... Or sli.. Usually there is no problems on way slower machines. Do you have vsync enabled or disabled? If it's disabled or display fresh-rate is really high - that might cause some problems too.
I've seen some issues caused by my recording software before. Pretty sure vsync is disabled, not using a compatible monitor. I've seen issues caused by 4k monitors before too.