I don’t have an answer, but you’re not alone. I have occasionally smelled the same weird, moist, musky, mucousy, (I’m feeling a bit queasy) smell before, too, when I sneeze. Sometimes it’s very strong, and (hold your stomachs, now)I have caught a whiff when my wife sneezes. EWWWW BLECHHHH! It seems to be worse when I have a cold or sinusitus, and I just always assumed it was what mucous membranes smelled like.
I was just wondering if this “smell” you experience is also experienced when water goes up your nose, such as when swimming/diving or laughing while eating/drinking.
It is perhaps a saline-like smell from the mucous lining, I WAG. Along these lines, often the mouth/nose can get an induced copper-taste/smell, respectfully, during certain instances usually associated with a mild trauma, in the least, I believe - can’t recall the exact circumstances.
Sometimes, when I sneeze (particularly if the sneeze was violent and unexpected), I notice a distinctly ‘musky’ aroma on my hands*.
When you sneeze, many times the sneeze comes through your mouth as well as your nose. My guess is (kinda gross) it’s the vaporized saliva, mucous, funk, etc. that you have in your mouth; when you sneeze, all this gets sprayed into the air as a fine mist, and you end up “smelling” it. I’ve noticed this “aroma” myself (it’s kind of “sickly sweet”), and with others, and it’s generally stronger if you haven’t brushed your teeth/tongue. Gick.