Object fell down AC duct

The plastic cap on a cardboard drink carton slid across the dash where I stupidly put it and my best guess is it dropped into the right AC vent. A day after this happened I heard a rattling almost as if a branch were caught under the car. It seems to have subsided but protectively I booked it into my Indy garage in a couple of weeks.

I suspect they can run a borescope down the duct and search for the plastic cap, then retrieve it with a flexible grabbing tool. What I cannot tell from looking at the hard-to-decipher schematic of the AC system is where the cap is most likely to have landed. (My first thought was the rattle I heard was linked to the fan movement, but as the sound vanished playing with the fan on/off and speeds did not bring the sound back.) I’d be delighted if it were gone for good, but my luck doesn’t usually run that way.

Any thoughts on where to look or if I can get into the right lower guts of the air blending system from below?

Thanks.

Eliot B.
Northern Va
2014 Gen 3 Prius Five