Learn Italian: Fanno un chiasso terribile quando russano. - They make a terrible racket when they snore.

While rumore is the general word for "noise" or "sound," chiasso specifically refers to a "racket," "uproar," or a loud, chaotic noise—usually caused by people, crowds, or in this case, very loud sleepers.

Since this lesson is about adjectives used as adverbs, is terribile acting as an adverb here?

No, in this sentence terribile is a standard adjective modifying the noun chiasso (a terrible racket). It ends in "-e", which means it is invariable for gender and stays the same for both masculine and feminine nouns. If you wanted to modify the verb to say "they snore terribly," you would use the true adverb form terribilmente (russano terribilmente).

Is fare chiasso a standard combination of words in Italian?

Yes! Just like in English where you "make a racket" or "make a noise," Italian uses the verb fare (to do/make) with chiasso and rumore. Saying fanno un chiasso is the most natural way to express this idea.

The verb is russano (they snore). Does this have any relation to the word for a Russian person?

Etymologically, no. The verb russare (to snore) is onomatopoeic, meaning it was created to imitate the actual sound of snoring. However, it does create a fun coincidence for language learners: the word russo can mean "Russian" but it is also the first-person singular "I snore".