First, I wanted to say I decided to join this forum after researching and solving several problems here. Now on to the issue.
Apparently, 4runner seats are notorious for a popping/creaking sound especially after a couple years of use. I first experienced the sound in my driver seat, which would happen during turns then starting and stopping. I ended up taking it to the dealer and having the entire frame replaced, which resolved the issue. I was fortunat to have an extended warranty with a $50 deductible that covered the $900 worth of labor and parts, but was hated not having a car for 3 days.
Recently I noticed my passenger seat started popping with every bump, turn, start, stop. I was able to narrow down the area to the bottem left hand side where the seat connected to the back rest, next to the center console. I could replicate the sound by gently tapping the back of the back rest from the back seat. Now on to the possible solution..
I removed the four star bolts securing the seat to the floor board, while leaving all the electrical components connected, I adjusted the back rest to the most forward and backward postion. Note; while lowering the back rest to the furthest back postion, the chair reclines almost flat. The bottom of the chair, where it is bolted to the floor, will lift up from the floor board. This reclined postion is not possible while still bolted, since the back seat will prevent it from reclining this far. During the reclining process the hinge of the back rest will pop and adjust where it is attached to the seat.
After moving the seat upright from the reclined postion, I removed it entirely from the car. I proceeded to tighten every star bolt and screw that were in view. The most important being the star bolts under the plastic side coverings where the seat and back rest meet. These can be distinguished from other screws, since they are the only other star bolts that are the same size as the star bolts that bolted the frame to the floor board. These bolts along with the star bolts underneath the seat tracks on the bottom of the chair (you must flip the chair upside down with the bottom facing you to see these) were noticeably loose.
After tightening all screws and replacing the seat; i have yet to hear any pop/creaks after 3 months, even with a passenger riding along. In short, I am not sure if the culprit was the tracks or the connection of the back rest to the seat, but the alignment of the back rest and tightening all screws seemed to do the trick. All in all the work took about an hour.
Hope this helps you fellow people suffering from OCD.