I'm still trying to figure out why they put it there. Felt totally random.
I definitely see what you're saying. While I totally loved it for the Disney-geek factor, I do agree that it was kind of a "what the hell?" reference that very tenuously makes sense. For me I was able to buy it as something like the ghostly echoes of fading life that one might here during the passage to the other side. In other films where a character is seen "passing on" they've shown flashes of memories or snippets of dialogue from that character's past (the "whole life flashing before my eyes" phenomena) so I took the black screened ride audio as bits of each of their experiences all running together as they each saw their lives flash before their lives on the trip over, and we (the audience) were just treated to a peek at those flashes.
I know it's not the strongest plot device, but to me it wasn't the biggest stretch as the story set it up as them journeying over to the other side by sailing over a gigantic lost waterfall, and compared to some of the other crazy stretches in the film this one was easy to believe.