96 dodge ram 5.9L singlecab GAS?

It's really hard to know exactly what it is without hearing it, here are a few likley possibilites. You may have something as minor as a weak hydraulic lifter, after the oil warms up it allows the lifter to pump up making the noise go away. You may also have a rod knock this is much more serious, a rod knock is caused by excesive oil clearance between the connecting rod journal and bearing. If this is the case the engine should not be driven, the oil pan should be pulled and the rod caps should be plasti gauged to determine which rod bearing is bad, more likley than not the crankshaft would have to be removed, machined, and oversized bearing installed. Another possibility is a piston wrist pin, or a broken piston skirt. From my experience with ebay a lot of people like to play dumb, they know exactly what the problem is and how major and costly it will be to repair, so they put it on ebay and say I think there might be something minor wrong with the car, but I'm not sure. Bottom line, worst case senario the engine will have to be pulled, machined, and rebuilt, and reinstalled. My guess 1000-1500 if you intend to do most of the work, Think more like 3000 if you plan to have someone else do it. If it is the oil screen It would have low to no oil pressure until the engine warmed and the oil thined out allowing it to p through the clogged screen. If the screen is 100% clogged the engine would have no oil pressure ever, and after about 5-20mins of running would seize. My guess is the pan could be pulled in a matter of a few hours to determine if the screen is clogged on not, and If he suspected this why hasn't he had the pan pulled and inspected, this would cost only a few hundred dollars at a shop and if it was the problem the pickup tube and strainer replaced $40 dollar part, or Cleaned (free) and he could be back on the road, instead of taking a 2-3 thousand dollar loss selling it on ebay needing repair. One time my friend bought a truck displaying the same symptoms as this Dodge, it to was a 4X4 truck, it had no rattle only low oil pressure. The cause was found to be the oil pan had been crushed and pushed into the oil pick up tube (while 4 wheeling I ume) This may also be the case, but if the car would have had a rod knock as well fixing the oil pan would not have made the rod knock go away. Good luck, if you live near the truck check it out before bidding so you can hear the sound yourself, or take a motor head friend of yours along, anyone with a fair amount of automotive knowledge will be able to distinguish a rod knock from a collapsed lifter.