squeeking noise

Have you checked the bottom part of the seat belt, I mean the part which is in the contact with the seat. Sorry I don´t know the word in English for that. There is a little "hook" and when the passenger is in the seat and the seat belt is fixed in to that part it moves a little bit and it creates squeaking noise-metal on metal contact. I had that problem so I isolated that little "hook" with rubber and the noise was gone.