In case you have you monitor in direct view to the headset and especially if this is a large one, you might want to turn it off too. The G2 cameras might be picking the moving screen content as a moving headset exemplifying any subtle movement.
Otherwise there is another subtle movement you can perceive sometimes but honestly only with Light House chirurgical precision tracking (light and days between the Index and the G2 - I own both - regardless of any progress inside-out tracking technical progresses). This subtle movement is the one due to your blood pressure in your bottom when seated making your body slightly jittering back and forth at the same rate as your cardiac pulse rate 