When you first land on the Island the Volume of that Thunder and lightning is positivly frightning. I liked it, no loved it… one of the people who I play the game with nearly lost bowel control (ohh how we laughed)
My suggestion is that As your character levels up the volume of the thunder should reduce based on how high your level is, so that at 60 it’s basically at where it is now.
It’s really atmospheric early on, the fear of the unknown, all the new animals and dangers of the island around you and as your character improves it’s signifies that becomming familiar with the sights and sounds of the island.
The rumbling thunder when a Maelstrom event is soon to start is absolutely realistic. There have been times when I was immersed in the game that I thought it was happening outside (not in my computer). That was fantastic.
One problem, however, is the ambient birds DURING the maelstrom event. Birds warn of an approaching storm (so they’ll sing before and after a storm), but they don’t sing out DURING a storm. I would recommend a ‘cancellation’ of birds that sing out during the maelstrom event. Its only happened a few times, but it does feel out of place.