Southern California is getting battered by rain. Last night I noticed a water sloshing noise when the car accelerates from a stop or came to a stop. It sounds like it's coming from the floor. I popped the rear passenger side carpet but it was dry. I checked the door drains but they were all clear. I also pulled that weird plastic plug out of the floor boards on the passenger front side but found nothing.

Where else could it be?

Is there a hollow in the running boards (like where the Frog hid the heroin in the French Connection)?

It really was like the French Connection. There is a plastic/rubber plug that is the only outlet to a 'running board' type compartment. It's located right next to where your foot would be while sitting in the car. I opened it and water came pouring out.

Those plugs are not the only exit, the water in that area should drain out of the bottom of the rocker panels.

Look outside under the bottom and you will see about four slotted openings that you need to clean out with a pointed object.

Then from the inside remove those plugs, there is more than one and clean out any leaves or debris. You can also remove the metal cup that holds the seatbelt reel to gain more accsses.

All of the water that goes into the cowl vents drains down to the rocker panels, so it is important to keep those bottom drain holes clear.
--
Bruce S. near D.C.

Maybe it's trapped in one of the frame rails.

Check your drains in the cowl area of the engine compartment, and also take a look under the seats for a half empty bottle! (Don't laugh too hard, I've shot myself in the foot on this one!) Good luck with the weather down there.

Check the A/C drain tube beneath the passenger side of the center console. In my 940, it can get stopped up with crud and trap enough water to produce sloshing and eventually dumps water on your passenger's feet when you take a hard corner. In my 240 a clog only resulted in a damp passenger side carpet.

Could your door drains be clogged?

They're all clear.

Trunk? Or could it just be a low gas tank sloshing around?

Are there any hidden parts of the trunk? I took out the carpet, the spare and the little aluminum plate on the passenger side and didn't find any water.

Gas tank is full.