The correleated noise observed disappears when the 1458 HV unit 2003 is turned completely off (it is still there when HV is set to 0), it seems to be slightly worse using the new pick-up boxes. The noise does not appear to be coming through the HV cables. We tried removing all HV connectors and taking HV from another unit - it is the closest 1458 that generates the noise. Attempts to set a common ground for the HV unit and the SWAMP crate did not reduce the noise. Removing the OM cable also removes the noise. This doesn't mean that the noise comes from the OM cable since this also changes the impedance of the SWAMP circuit, however moving the connected OM cables away from the HV unit reduces the noise considerably. Probably the higher noise rate attributed to the new pick-up boxes come from us changing the geometry of the OM cables when installing the new boxes.
