There's one thing about squeeks in floors - they always seem to get worse and more grating. I don't have any answers as to the repair, but I'd be making darned sure the dealer resolved the problem. I bought a brand new 82 Camaro that had a squeek/rattle in the back. I hounded the dealer until they finally figured it out, 10 months after I'd bought it. A bracket up under the back window had been improperly welded at the factory and had it been left as is we'd of had one heck of a rear window leak down the road, I suspect the day after warranty was up.
Good luck, and let us know what the resolution is. I'm wondering if this is a problem others have noticed or just an issue with yours.