The Quad Cortex outputs 1 and 2 (XLRs) will ground to the device that the XR is plugged into (e.g. a grounded audio interface). When using a 1/4” cable from outputs 3 or 4, there is noise if and XLR is not also connected to a grounded device.
To address those situations where I am not using the XLR outputs, the noise is bugging me, I wired up an XLR plug to connect the ground pin of the XLR to the ground pin of an electrical plug. This stops the noise by connecting the Quad Cortex to ground.
Posting here in case this help others with the same issue.
