Water leaking into quarter panel

I have a 92 S-10 Blazer, 4x4, Tahoe 4 Door. Somehow, water is getting into the right quarter panel and holding there, so when I brake or accellerate I hear the water sloshing back and fourth. Anyone else ever have this problem? Are there any drain holes that are possibly clogged and where are they? Any help would be appreciated!!!

Are you sure it is in the quarter panel ? There should be holes in the bottom. If it is in the quarter panel, get a wet/dry shop vac and stick the hose down through the panel from inside the engine bay.
It may also be in the cowl space between the front of the door and the fender (where the wiper mechanisim is. That space is open to the elements and there are drain holes in the bottoms on both sides. Make sure those are clear.
I am re-building a 84 S-10 pickup and found those holes completely blocked with leaves and crap.