Squeaky rear seat

[Drumtian]

I have a 6 months old California which has developed a loud and irritating squeak sound which I’m sure is coming from the rear seat/bed. I’ve emptied the van to ensure it’s not something I’ve put in!
It’s likely something I can get fixed under warranty but wondered if any of you California veterans had experienced this and could suggest an easy, quick fix to save a garage visit.
It’s happening at all speeds and is worse as you’d expect depending on road surface conditions.
Any thoughts gratefully received!