2014 Hardtop - water in quarter panels

I recently started noticing water sloshing in the rear panel behind the pass door and ahead of the rear tire. It happens after going thru a car wash or a heavy rain, usually goes away in 24 hours. (depending on how long it rained) I can see drainage (very slow) on both sides ahead of rear tires for a long time after rainfall. (I notice this once the car is dry and parked on dry pavement) Carpet appears dry. It seems there are many talking about this (on other sites) but no real direction on where I should start looking. Although I realize I need to drain the water out of these locations, my gut tells me that the water shouldn't be here in the first place. Is it supposed to be draining someplace else, that may be clogged, and ending up in here instead? Anyone found a source for this problem?

Fixed! I took out backseat and both interior side panels. After removing seat belt spools to gain access to the voids in front of the rear wheels, I found a lot of water in each side. At least a half gallon per side. Now to figure out how it got in there. I used food coloring and made 4 different colors, a gallon of each. I started with the gap around the trunk lid using red. Nothing noticed inside the car. Then the gap along side the rear glass with green. Nothing. Then I used blue into the gap around the read side quarter glass. Bingo! Standing water in car turned blue. Repeat for glass on drivers side. Identical result.
With an 3/8" x 18" drill bit, I was able to drill a hole in the bottom of the voids (thru the standing water from inside the car). The bottom was not steel, plastic maybe?. All the water drained out of both sides. I completely dried the cavities and left the interior apart for a few days to air dry them further. I called a local glass shop, they ordered new glass for both sides and are replacing/resealing them Friday. (they probably could just reseal them, but insurance glass coverage requires replacement). Just happy not to hear the sloshing anymore!