2019 Lexus RX350 with 70K miles; no modifications; auto trans; no codes.  Still under CPO warranty from Lexus (not aftermarket warranty).  Car has automatic parking brake, if any consequence.

Video here:  https://youtu.be/eEteoK5qWUg

Another video of just the training control arms:  https://youtu.be/ODvrFiIUg3A

The best example of the "clunk" from the video is the first time I backup and you hear it (not talking about the automatic parking brake disengaging....that has a "whirring" sound and is not what I'm referring to).

Summary of issue:  When backing up slowly then hitting the brakes moderately, you hear a clear "clunk", but don't feel it in the steering wheel or anywhere else.  When going forward and hitting the brakes to a stop, you hear the same thing.  Inspection of the rear suspension doesn't show any clear signs of faulty wear, etc... but something is amiss.  Wondering if possibly the rear trailing control arms, but bushing seem in good shape and not moving when video'd with camera trained on them.  Sway bar bushings seem in good shape and sway bar links didn't appear to have any play.

The clunk clearly happens when you see the car force the suspension downward as the car brakes when going backward.

Noticed this after I did some brake work on the rear pads where I greased the shims only, but I didn't replace the pads and the only screws I removed and reinstalled were the caliper mounting bolts (14mm bolts).  I have done this work before on our other Lexus with no issue, so not figuring this is the problem and not sure what the problem would be.

Any thoughts are appreciated.