Is there any chance of an obstruction in the track of that seat? I know it sounds insulting but I confess I had a screw loose in the old seat and it squalled like a goat. It was between the rollers that can't be seen unless the seat us upside down. Evidently the rear roller moved it forward without much noise but the front roller made all the racket.

I didn't figure out the problem until I bought the 'new,' seats.

Luck!