MEG Artifact Identification

Hi everyone,
I just wanted to use some of your eyes to see if anyone could help me identify a potential artifact and if it is worth removing or not. I keep seeing this particular large drift in the magnetometers in the back-bottom most part of the MEG helmet, along the back of the neck area.
Epoch is 4sec long, filtering is 0.5-120hz, scaling on the plot is 2000fT. Any Idea what is the underlying cause of this in most if not all the participants? I am not sure if there some underlying brain activity that is causing it or if it is purely artefactual. I figured if it was from neck muscles there would be a bunch of fast activity with it, but, as you can see that is not the case. There is also another similar large drift at the back right of the helmet that is pretty consistent with most if not all participants too.

Any insight is appreciated,