Stop obsessing. You're on a vacation, or maybe even a trip of a lifetime, and you don't need to fret over something that doesn't matter.
I'm not saying to ignore it, so spin the wheel unloaded and make sure the hub isn't binding, and that nothing is brushing the spokes, because you don't want the front wheel to lock up.
But if the wheel spins free, and you don't see what may be a safety isues, ignore the sounds until/unless it changes or gets worse. Given that oil at the nipples, and/or tightening the wheel slightly changed it, you can reasonably assume it's spoke/nipple/rim related. As such, it'll either be OK, or there's nothing you can do about it anyway.
So keep an eye (ear) on it, but put it in the back of your mind and focus on enjoying your trip.
BTW - don't use more oil on the nipples which only serves to mask rather than solve the real issue (if there is one).
Have a great trip, let us know how things turn out when you;re back home.
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