meaning - Usage of する for the five senses - 音がする, 匂いがする, etc

Do these type of expressions mean that something is being perceived or that something is producing said sound/smell/etc?

For example, in the Weblio website I saw "門を叩く音がする" translated as "There is a knock at the door". But "足音がする" is translated as "I hear footsteps."

So does "音がする" mean "(I) hear a sound" or "There is a sound/(Something) makes a sound"?