Had some time to come back to the issue.
3DS Max is definitely exporting it like that. Because when I re-import the FBX into Max I get can see the shaking.
I have tried some of the obvious option settings like baking and all that. No dice yet. I also found another animation it does it on.
EDIT
Okay, only for SOME animations when I reimport them do I see the artifacts in 3DS Max. Others are fine in Max on reimport but shaky in UE.
This is going to be a rough week… lol
EDIT 2
So, it turns out you can smooth the high frequency jittering by baking the animation with a sample step of 2 instead of 1. Obviously you lose some fidelity, but at this point I’m happy enough.
Also, it seems like my issue is similar to this issue:
for what it’s worth.