2001 Oldsmobile Bravada liquid splashing

I have the same issue and haven't been able to isolate it.

First, I thought it was my spare antifreeze in the back splooshing around in the bottle. Too much "drag out" in the sound, though - no way water in such a small container could make that noise.

Then, I thought it was maybe gas in the tank, but that doesn't make a lot of sense. How could I hear it while I'm driving?

I think it's rainwater that has leaked into the chassis and sloshes around in there until ti evaporates.

Have you ever had water leaking into the cabin through the seals on the driver door, or perhaps in through the sunroof?

We have had a lot of rain recently and that could be it, but I haven't noticed any water leaking in the cabin. Where does the water drain out or is there a way to unplug it.