A trilha sonora tem ruído de fundo.

Because trilha is a feminine noun in Portuguese, so it takes the feminine article a. The adjective also has to agree with it, so you get sonora, not sonoro.

• a trilha
• a trilha sonora

Also, trilha sonora is the normal fixed expression for soundtrack.

In Portuguese, adjectives often come after the noun. So trilha sonora follows a very common word order: noun + adjective.

That said, some adjectives can go before the noun in other contexts, but with trilha sonora, the usual and standard expression is exactly this order.

Tem is the third-person singular form of ter, which usually means to have.

Since a trilha sonora is singular, the verb is singular too:

• A trilha sonora tem... = The soundtrack has...

If the subject were plural, the verb would change:

• As trilhas sonoras têm...

Because ruído de fundo is being treated as a general, non-specific thing, like background noise in general.

So:

• tem ruído de fundo = it has background noise

If you say tem um ruído de fundo, it can sound more like you mean a particular noise or a specific unwanted sound.

Both are possible, but they are slightly different in feel:

• tem ruído de fundo = general background noise
• tem um ruído de fundo = a particular background noise / a noticeable noise

De fundo means something like in the background or background.

So ruído de fundo is literally noise of background, but in natural English we say background noise.

You will see de fundo in other expressions too, such as:

• música de fundo = background music
• imagem de fundo = background image
• papel de fundo = background paper / backdrop, depending on context

Both can relate to noise, but ruído is often more technical or more precise for unwanted sound, especially in recordings, audio, electronics, or sound quality.

• ruído = noise, interference, unwanted sound
• barulho = noise, loud sound, commotion

In a sentence about a soundtrack or audio quality, ruído sounds more natural and specific.

Ruído is pronounced in three syllables: ru-í-do.

The accent mark shows that the stress falls on í, and it also helps show that u and i are pronounced separately, not as one blended sound.

A rough Brazilian Portuguese pronunciation would be:

• roo-EE-doo

The initial r in Brazilian Portuguese is often pronounced like an English h or a guttural sound, depending on the region.

Yes. That is a perfectly good alternative.

Compare:

• A trilha sonora tem ruído de fundo.
• Há ruído de fundo na trilha sonora.

The first one is more direct: the soundtrack has background noise.
The second one is more like There is background noise in the soundtrack.

In Brazilian Portuguese, tem is very common in everyday speech, while há can sound a bit more formal or written, depending on context.

No. Trilha sonora can be used for the soundtrack of a film, TV show, game, series, documentary, and sometimes other media too.

Depending on the context, Brazilian Portuguese may also use som, áudio, or more specific terms, but trilha sonora is a very common general expression for soundtrack.

If the subject becomes plural, the article and verb change:

• As trilhas sonoras têm ruído de fundo.

Notice:

• a → as
• trilha sonora → trilhas sonoras
• tem → têm

The circumflex in têm helps distinguish plural they have from singular tem.