@verlakasalt While not fully, the HQ setup that I use does provide a bit of EMI shielding. The sensor mount and also the T2 tubes are metal. The Rpi4 enclosure is all metal as well.
Given that you replaced the cable, and in the absence of EMI issue, then it may be the sensor. What comes out of the sensor to the RPi is already digital, so the interference or defect would likely be in the sensor conversion itself, or in the power (or power reference) of the A/D.