It's possible there's another sound that we don't hear or was messed up and doesn't play, but after the roar Dinklebot says:
I don't even want to know what they're keeping down there.
English
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Wait nope. Messed up missions sorry
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Yeah, there was another mission where it goes off at the same place, but for the strike he totally has it backwards. I figure the roar is supposed to come first, hence the Ghost going "Sounds like we're getting close."
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You know what I think I've heard it both ways. Roar first and second. So it may be a matter similar to the Tanniks strike. If you move too quickly the order gets messed up.