Hey guys,

2017 S63 with rear AC. When the rear AC is on here in Florida, I notice a clunk/bump type sound and movement under the driver floor board sporadically.

Its almost like a gear or flap is engaging. Any ideas what this could be?

 

On my Maybach there was a selection for the air to come out of a vent under each of the front seats OR on the B pillar. I have a suspicion your hearing the vent flap closing one one of the floor vents. The noise could be because some debris has gotten into the floor vent and is causing the door to make noise when it actuates.

I would sit in the car running and acuate the selection between the b pillar and the floor vent and I would also check the floor vents for anything in them. They are at the back and beneath the front seats.