I found this sentence on the British Council website. I don't know why "the" is used in the sentence because all of the nouns seem indefinite:
Imagine a beach; a quiet place, with only the noise of the sea and the gulls in the background.
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Once you restrict the sentence to the beach that you're imagining, all the related objects become definite -- you're referring specifically to the objects related to that beach. So it becomes "the sea" because you're only talking about the one sea connected to that beach, and "the noise" because it's just the noise of that one sea.
As soon as you say Imagine a beach you can refer to things usually found or associated with a (any) beach using the definite article.
The same for anything: it was an old house and the front door creaked and the walls needed painting and the roof had holes in it and the owner was nowhere to be found.