After a lot of searching, I believe I have traced the noise of something rolling about my truck to the vents that run under the driver seat into the back seat. Maybe someone kicked something into the opening, or..... I dunno. The sound is driving me nuts though.

But the more important question, short of pulling the seat out and removing the duct, any tips on how to get the pebble out of there?

Thanks.

Try hitting the vent with a shopvac. I dumped over a bag of peanut M&M's on one road trip and it was amazing the amount of noise they can make under the drivers seat!