In a sagittal view you can even see the pulsations transmitted into superior sagittal sinus. Loads of pulsation in midbrain. Note also the evident non-linearity.

So you do “physio correction” in your “de-noising” pipeline, eh? This is a single EPI slice acquired at 25 fps. Lots of dynamics just from the arterial blood pressure wave! How well does your “de-noising” really do, do you think?