That is so weird. Same thing happens to me... Especially after I gained a lot of weight from working with computers for all these years.... I don't think it's anything external that is causing the squeak. I think it's some of the metal reinforcements inside the seat itself that when you shift your body from side to side, causes the squeak. In the summer, when I maintenance my baby up.. I'll see if I can wrip the seat apart and see if I can find what the problem is...