You can see the weld seam and the notches, those two notches are where the drain holes are located.

 

And if it is on the passenger side, check the rubber drain hose for the AC evaporator. It comes out of the firewall and into the engine compartment and angles downward. I used compressed air on mine to blow it open once and all sorts of algae/mildew material came out. It was making a sloshing sound.

 

I should check this one myself. I have only tried the A/C out a couple times and have not noticed any issues, but right now I'm on a drain clearing kick. I'm trying to find a way to check the rear drain from the top. Is there a way to access the top of the rear drain without removing the top completely? I have tired bracing the top halfway folded back and still cannot seem to find the drain...

 

I will have to give this a try. Sounds like it could be the solution to my sloshing noise. Will keep you posted if it works. Thanks for posting the information. I didn't even realize those drain holes were there until you mentioned them.

 

It is outboard of the seatbelt tower on each side. There is a cup with a drain in the middle of it that the rain rail dumps into. It is definitely easier to see with the top removed, haha.