I had a similar noise. However - in our case it was not the seat itself. The squeak was coming from the left rear seat belt holster that is attached to the pillar.
At first I thought it was the belt mechanism where it loops behind the trim piece. However - before taking any apart - I tested the other 3 primary seat belt holsters and none made the noise.
I lifted the plastic trim that covers the holster (the one that is part of the button you pull and push to slide the seat height adjuster belt up / down) and sprayed some NON-staining petroleum lubricant.
This helped but the noise was not gone completely. So I pulled on the actual button - I pulled up and it had enough room to allow the nozzle-stick on the spary bottle to sneak in and sprayed some lubricant in there. Under the button there is a push-pin that is metal. This when pushed or pull allows you to slide the adjuster on a track. Because I pulled it up and sprayed into it - it not only sprayed the push-pull pin mechanism - but also managed to get into the track and surrounding moving parts.
Now the noise is gone. No more squeaking.
When you do this - take a shop towel and put it opposite of the area you are going to spray to prevent overspray from landing on other trim and leather surfaces. Make sure to wipe off any excess that may trickle down the holster and down onto the belt itself. And of course - look for NON-staining petroleum based spray.
Some said - try white lithium because it does not have a scent. And I agree - white lithium spray is odorless but it is messier and it dries whitish. The key to avoiding odor is to allow your car to vent, avoid overspray and of course - wipe down any overspray, clean the areas not intended and freshen with a neutralizer.
Good Luck!
