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Latch bolt on the frame (where the latch assy meets the door post) could be loose, the screws (3) might be loose to the point that it rattles when you hit a bump in the road. I've seen bunches of these that when the become loose, the wear on the latch bolts cuts a groove into it, making it rattle even more... replacement or tightening it up with a drop of locktite on the threads will keep it from coming loose again ( just untighten one at a time so as not to get it out of alignment and put a drop in the middle of the threads of the screw) Sometimes the wear will be noticeable and not very many people look at their bolt latch assy's very close to know what to do with it. So now you know.
Worn dorr hinges will also create a rattle. If you notice your door drop a bit when you open it, and it can be a pain to close(requires slamming or a very hard pull/push depending on in or out of the truck) then those are likely the cause. Hinges out of alignment will not help this much either. To check hinge alignment, simply look at the gap between the door and the cab pillar(from outside the truck, as well as the gap between the door and the fender/hood area. Both will indicate an alignment problem, this gap difference will also indicate worn hinges, and is easier to see if the door is opened slowly, and closed slowly. Try pushing the door gently, till it almost latches, and then give it a quick shove, and watch it to see if it lifts up. This would be the definitive worn door hinge problem. I've been able to cure the door latch post problem simply by wrapping a small bit of duct tape around the door latch post to replace the platic that wore off...it's a temp fix, and you have to find the magical thickness...it will only last as long as it takes until you either need to do it again, or replace the latch posts. Checking the door latch for loosness is another good idea, as previously posted. I would take this a step further, and tighten all three screws to put it into alignment, and then take one out, add blue loc-tite to it(removeable without heat, but will hold very well) and then do the next and the next, until both sides are done. Red loc-tite is designed to be removed with heat applied, and is never a good idea where heat can't be applied without possibly damaging something(like paint) Use blue where hand tools are applied regularly, use red where you'd likely use an impact, or on high stress points that you can apply heat to before using hand tools.
my 84 has the same exact problem, and the prior owner changed the driverside latch hook and that side stopped, cuz when you close the door youd have to slam the hell out of it, and even when it closed properly when i'd go down the driveway the passenger side would rattle.