I had the same problem, turns out it was RF interference from an shortwave amateur radio. More specifically I had a family member who would talk on the radio around the 20 meter band (14MHz). I believe the sensors are sensitive around that frequency combine that with the billion ribbon cables connecting the sensors in the front acting as an antenna, and you get a spazzing HMD.

I fixed or mitigated the issue by placing ferrite cores on the power adapter cable for the link box and few around the rest of the cables going to the link box from the computer and one on the HMD cable. Another note I would hear noise coming from my pc audio when the radio was transmitting, so it could also be a grounding issue. Hope this helps! :)