I am getting that musty, dusty attic or insulation smell from by A/C vents, and it is more pronounced when very hot outside.
To paint a proper picture . . . the house is only 2 years old and has dual-zone cooling. The upstairs furnace is in a small part of the attic where the insulation is rolled. The rest of the attic has blown insulation. Because the "blown" side represents the largest part of the attic, most of the return and supply ducts run to it from the "rolled" side.
Last year, to help with costs and efficiency, we had additional insulation blown in to the "blown" side. Since then, the A/C has smelled like the attic, though we notice nothing from the heat in the winter.
I recently when up there and taped up all the joints, nipples, and boots so minimize cold air blowing into the attic (or being sucked from the attic). The contractor had failed to do this. I checked the ducts, and none have fallen loose or broken (all have R6 insulation around them). I had the original A/C contractor back, and he claims no insulation is collecting on the coil (I don't know how to check this myself).
We have ridge and soffit vents, though I noticed that insulation has made its way into (and blocked) several of the soffit vents.
I am not saying the A/C ducts are now air tight, but I certainly did as good a job as most contractors would do. I don't think I can put any more foil tape on the ducts! Any ideas? Could the lack of ventilation in the attic be the culprit? Is there something else to check on the furnace?