Sloshing sound

I recently bought a 97 Honda Passport 4WD 5 spd and I've noticed what can be best described as a liquid sloshing sound emanating from the front passenger side when I first drive it in the morning and go over any bumps. The sound disappears after a few minutes of driving and doesn't effect drivability. I first thought it might be the washer fluid but that wasn’t it. BTW, I live in Arizona so I can't imagine rain water collecting somewhere inside. Any ideas?

I am also wondering if there is a light behind the a/c, heater controls since maybe the bulb has burned out. I thought I might be able to see the bulb once I removed the ash tray assembly but no luck.

TIA...

check to see if your doors are draining. Run a wire up into the drain holes in the bottom of the door.

Thanks for the suggestion. I will try it out after the rain stops pouring down ;-)

There are also a couple of weep holes in the pinch weld under the door sill. The one closest to the front of the vehicle on the passenger side of mine was clogged with debris and not draining awhile back. I think I stuck a small drill bit up there and the water came pouring out.