Mis amigos se enfadan cuando hay tanto ruido en la ciudad.

In Spanish, enfadarse is a pronominal verb that means to get angry / to become angry.

• Mis amigos se enfadan = My friends get angry / become angry.
  Here se is required as part of the verb enfadarse.

Without se, enfadar usually means to make someone angry:

• Ese ruido enfada a mis amigos. = That noise makes my friends angry.

So:

• se enfadan → they get angry (they change state)
• enfadan → they make someone else angry

• Enfadarse focuses on the process of getting angry, the change:

  • Mis amigos se enfadan cuando hay tanto ruido.
    My friends get angry when there is so much noise.

• Estar enfadado describes the state of being angry:

  • Mis amigos están enfadados porque hay mucho ruido.
    My friends are angry because there is a lot of noise.

So the original sentence emphasizes what causes them to become angry, not just the fact that they are currently angry.

The verb agrees with the subject:

• Subject: mis amigos → they, 3rd person plural.
• Verb: enfadarse, 3rd person plural present → se enfadan.

If the subject were singular, it would change:

• Mi amigo se enfada cuando hay tanto ruido.
  My friend gets angry when there is so much noise.

Hay means “there is / there are” and is used to introduce the existence or presence of something:

• Hay ruido. = There is noise.
• Hay tanto ruido. = There is so much noise.

Ser (es) is not used in that structure. Es tanto ruido is not correct Spanish in this context.

Typical patterns:

• Hay mucho tráfico. = There is a lot of traffic.
• Hay demasiada gente. = There are too many people.

Both indicate a large quantity, but they feel slightly different:

• Mucho ruido = a lot of noise, neutral quantity.
• Tanto ruido = so much noise, often with more emotion or complaint, implying it’s excessive.

In this sentence, tanto fits well because your friends are annoyed; it suggests the amount of noise is too high from their point of view.

In Spanish:

• tan is used before adjectives and adverbs:
  • La ciudad es tan ruidosa. = The city is so noisy.
• tanto / tanta / tantos / tantas is used before nouns:
  • Hay tanto ruido. = There is so much noise.

Since ruido is a noun, you must use tanto, not tan.

• en la ciudad = in the city → describes the location of the noise.

  • Hay tanto ruido en la ciudad. = There is so much noise in the city.

• de la ciudad would mean of the city / from the city, and suggests origin or type:

  • el ruido de la ciudad = the noise of the city / the city noise.

Both can be correct in other sentences, but here en la ciudad is better because we are talking about where the noise is.

Cuando hay tanto ruido describes a general, habitual situation:
Whenever there is a lot of noise, this is what happens.

For general facts or repeated situations, Spanish uses the present indicative, not the subjunctive:

• Me canso cuando trabajo mucho.
• Se enfadan cuando hay tanto ruido.

You would use the subjunctive after cuando when talking about future or uncertain actions:

• Se enfadarán cuando haya tanto ruido.
  They will get angry when there is so much noise.

Yes, there is a regional preference:

• In Spain, enfadarse is very common for to get angry.
• In much of Latin America, enojarse is more common:
  • Mis amigos se enojan cuando hay tanto ruido en la ciudad.

Both verbs are generally understood everywhere, but if you’re focusing on Spain, enfadarse is the more natural choice.

Yes, but the nuance changes slightly:

• Se enfadan por tanto ruido.
  Focuses on the cause: They get angry because of so much noise.

• Se enfadan con tanto ruido.
  Also expresses cause, often with a sense of annoyance due to that amount of noise.

• Se enfadan cuando hay tanto ruido.
  Emphasizes the situation or time: They get angry whenever there is so much noise.

All are grammatically correct; the original version highlights the habitual situation more clearly.