Not only Gaban was able to perceive them across the island (remember, Elbaf is not your average Joe island size), Elbaf is a HUGE ass island meant for Giants to live on.
So the fact that Gaban was accurately pinpoint where the Holy Knights are and how many there are is crazy work.
What's crazier is that the Holy Knights completely hide their presence or at least, "erase" their presence somehow so Luffy, Zoro, Sanji, etc. are not even aware of where they are. Gaban is the only one that knows where the HKs are.
And Gaban talks about a strange "voice" that can't be hidden, I wonder if Gaban is talking about one of the HKs or a completely different voice?
Anyway, thoughts?