I'll occasionally hear things when falling asleep, just as I'll also see some imagery when falling asleep (I'm also unable to visualize). So I assumed the snippets of sound I would hear was what people heard normally, just as I'm assuming the snippets of imagery would match what people normally see when they visualize. The sounds I hear (infrequently) sound like something in the environment, though it's clearly not.

So now I need to rework my assumptions. Thank you for letting me know. Language is terrible for conveying this type of information.