Fixed the creaking and rubbing issue of the Versus rear diffuser. The mounting height was the culprit. I couldn't figure out the actual rubbing point (turns out it was on the rear anti-sway bar) until we actually took the rear anti-sway bar off. I didn't figure it out until then because they were so close together that it was impossible to see between them without doing that. Did that today with lots of help. The three bolts that mount the diffuser to the single bracket next to the anti-sway bar were clipping it badly going over speed bumps, driveways, or just leaving my garage. The clearance of the bracket and the sway bar are different when the car is on jacks as opposed to sitting on the ground.
The third bolt (closest to the passenger side) was just....gone. Our best guess is it completely sheared off at some point (red arrow). The other two bolts were still on tight....although I couldn't take them off with the Allen key, as they rubbed down so much that the hole was totally deformed. After we got those off, we pushed the diffuser as high as it would mount. Also, mounting the diffuser on the rear of the bracket, as opposed to the front of the bracket, in order to give just another mm or two extra clearance for the bolts to be away from the sway bar. Took it out for a test drive. Quiet as a quarantined church mouse. Thank God that's dealt with and over.