Weird noise after shocks/struts replacement

Noises can be hard to track down. I have a couple different systems, a chassis ear that uses piezo sensors to "listen" to vibrations from loose/worn parts and a couple cheap digital recorders that I set in the area of the suspected noises.

For the noise you have. Toss some weight in the rear seat and see if the noise changes or goes away. It could be the seat retainer clips or something loose under the seat. It could be that the other noises masked it and now you hear it because they are gone.
It is also possible it is something in the trunk or in the door and it is telegraphing the sound.
You can also just feel around and push/pull on the trim, seats etc and see if something is loose.

Could be easily. Toss some weight on it or stuff something under it and see if the noise goes away. If it does pop the seat out and see what is loose. Could be a bad latch or bent support or?

That should work. Keep us in the loop.

Those come out real easy. Push the seat toward the rear of the car while lifting up. Then tip it up and pull it out. That will let you check to see if the latches are bent. From the motion of the seat you showed I am going to bet the tabs are bent and letting the seat bounce as you drive.

Really could not hear anything. However, if it sounds like a creaking video and they just changed out the shocks/struts it could be a bushing creaking. That can be a common thing if a suspension bushing it work and twisting in the socket or if a bushing was not tightened down with the vehicle weight was not on it. You could take a can of silicone spray and spray the various bushings to see if you can stop the noise but that would be a temporary thing.
Common bushings that creak would be the stabilizer bar mounts, the A arm bushings and the strut mount. You might want to visit the shop that did the work and let them see if they can find it. It is possible that it's something that would be covered at no cost.

That sounds like a bushing then. With the added weight the bushing compresses and cannot move. It could even be that a nut/bolt is not quite tight enough and it is letting the rubber move and squeak. But as it did not make that noise before the repair I would give them a chance to fix it before tearing into it myself.

That is the question. I would look at every one they replaced. If the noise was not there before those would be the place to start.

Look over all the bushings, including any that were replaced. You are looking for twist or cracks in the rubber or areas where the paint around the bushing is rubbed off indicating contact. It also may be that you cannot get the lube into the area that is causing the noise. However, it also possible that the noise is related to whatever is causing the lean/pull in your other post. It almost has to be bushing related as you said that having someone in the seat stops the noise. I guess it could be that a trim piece is creaking but setting in the seat will not usually stop that unless the person is setting on the trim.
Does the noise go away or change if they set on the other side?