fears?

Gavin has been having trouble going to sleep recently, no matter if we start in his room or downstairs. So even though he was sleeping better with the light off in his room, I wondered if he was becoming scared of the dark, so we've left his light on again some nights. I still don't know if he's scared of the dark, but he does seem to like the light being on.
He has a sound machine in his room that you can set different sounds, and Terry started it on the sound of ocean waves, which Gavin has gone to sleep really well to in the past, but tonight, as soon as we put him in his crib, he burst out crying. I thought it was just because he wanted to continue being held. But, since Gavin has been falling asleep to a different sound recently, I mentioned to Terry that he could change the sound machine to the "rainforest mode" which is the sound of birds of the rainforest, since Gavin has been sleeping well with that on recently. He settled right down, so I'm thinking for some reason maybe the ocean sound was scaring him. That's what it seemed like. I hear from other moms of 2 year olds that they develop fears around this age, and maybe that's part of the problems we have with him sometimes. I guess we won't know until he gets to talking better so he can tell us.