Aragorn in Moria?

[Legate of Amon Lanc]

Originally Posted by The Might

We know that already in 2480 Sauron began to people Moria with his creatures, also as mentioned in the Tale of the Years, so it makes sense that Aragorn went in to take a look and see what the situation was.

Well, I think that's actually a pretty good assumption. The problem of Sauron and Moria was actually far bigger than it seems on first sight: it's not just about some wild mountain Orcs, but Sauron had a great interest in getting to Moria. It's not much about it, just hints here and there, but:

Originally Posted by LotR, Appendix A III, Durin's Folk

It came to pass that in the middle of the Third Age Durin was again its king, being the sixth of that name. The power of Sauron, servant of Morgoth, was then again growing in the world, though the Shadow in the Forest that looked towards Moria was not yet known for what it was.

(emphasise mine)
It's obvious that Sauron had some special interest in Moria, why, I cannot say. Perhaps for mithril? Nevertheless, it is known that apart from the "native" Orcs, Sauron actively participated on populating Moria with his own Orcs, apart from the "normal" ones, as TM already mentioned. So the idea of Aragorn's "enspionage mission" looks quite logical.