Sounds like it is an exhaust misfire or backfire and you may have a leak in the exhaust. The leak may be near an Oxygen sensor which will make the engine run rich and make the problem worse and eventually ruin the sensor causing even more problems. As there are other possiblities, such as if you are saying something is loose and making a popping noise the tranmission mount make be loose or you need to replace the universal joints. I am going to give you a walk through diagnostic for engine that are back firing. it is a good tool as it goes into depth that I cannot cover here. Just follow the link below;
Thank for the fast responds, but this popping sounds more like a gear slipping and is coming from the transfer case or the tranny thanks again
March, 10, 2012 AT 8:41 PM
Your very welcome. If that is the case it could be a mount for the transfer case, did not know it was AWD, or a busing and still could be a universal joint. If it is internal, you would probably have some shifting problems accopyaning the noise such as hard shifts or slipping between shifts or when in gear. The transfer case behaves differently though. Interanl damage to it would cause a loss of power to the front or rear axle and then the pop might be it re-engaging the axle. You might still be able to feel if there is a change in the way it handles or drives and the one axle that gets let loose might spin a wheel. However, if it were this severe of an internal issue, the van would have some sort of problem driving or change in the way it performas and I would expect it to fail completely very soon.
Otherwise I still think it is a mount, bushing or u-joint.