Marble(s) rolling under front passenger seat

Thur, 10/15, I purchased a Prius 2012 IV with 157K on it. I’m hooked. I love the vehicle and all the good information that comes with it through chat rooms such as this one and YouTube. This past Wednesday, I took the vehicle to my local Toyota dealership for an oil change and courtesy inspection and the vehicle passed with flying colors.

On Thursday, I noticed something rolling under the front passenger seat back and forth as I accelerated or took a brake. I thought it was something just rolling under the seat or positioned within the passenger door cupboard holder that was visible and could easily be discarded. To my dismay, I could not immediately see what was rolling. After a deeper look under the passenger seat, I found 4 marbles wedge within the left side seat floor track. I thought that was the culprit. Needless to say, there’s still one or two marbles rolling around under there within the heating vents (?). I found a post from several years ago where beads were rolling around within the heating vents and the recommendation was to, when safe to do so, put the heat and blower fan on full blast, floor the accelerator and move for 11 seconds and brake. The beads should come out from heat vents.

Well...this didn’t work for me and the sound is driving me nuts. Help!!! Thanks in advance.