Les avisa del zumbido antes de que evalúen el tímpano.

Les is an indirect object pronoun, meaning to them or to you all.

The verb pattern is:

avisar a alguien de algo = to inform/warn someone about something

So in this sentence:

• les = to them / to you all
• del zumbido = about the buzzing/ringing

Why not los/las?

Because avisar here is treating the person as the indirect object:

• Le/les avisa del zumbido = He/She warns him/her/them about the buzzing

In practice, with avisar, you may sometimes also hear direct-object usage in some varieties, but le/les is very common and standard for this kind of meaning.

The subject is not stated explicitly, which is very normal in Spanish.

Avisa can mean:

• he warns / informs
• she warns / informs
• you warn / inform (formal singular: usted)

So without context, avisa is ambiguous. Spanish often leaves the subject unstated when it is understood from context.

Because de + el contracts to del.

So:

• de el zumbido → del zumbido

This is a standard contraction in Spanish.

Compare:

• de + el = del
• a + el = al

But this only happens with the article el, not with pronouns. For example:

• de él = not contracted, because él is a pronoun

Because antes de que is followed by the subjunctive.

So:

• antes de que evalúen = before they evaluate / before you all evaluate

After expressions like antes de que, Spanish normally uses the subjunctive because the action is seen as pending, anticipated, or not yet completed at that point.

That is why you get:

• antes de que evalúen not
• antes de que evalúan

Evalúen is the present subjunctive form of evaluar.

Here is the contrast:

• evalúan = present indicative, they evaluate
• evalúen = present subjunctive, that they evaluate

The accent also matters:

• evalúan has the stress pattern of the indicative form
• evalúen is the subjunctive form

So the sentence uses evalúen because of antes de que.

It can be either, depending on context.

Evalúen can mean:

• they evaluate
• you all evaluate (ustedes)

Since you are learning Spanish from Spain, this is worth noting:

• In most of Spain, vosotros is used for you all informally.
• So if the speaker were talking to a group informally in Spain, you would often expect evaluéis instead of evalúen.

That means that, in Spain Spanish, evalúen often sounds like either:

• they evaluate, or
• you all evaluate in a formal register (ustedes)

Because Spanish often omits subject pronouns when they are not needed.

English usually says:

• He warns them...
• They evaluate...

Spanish often just uses the verb form:

• avisa
• evalúen

The verb ending already gives grammatical information, and context usually tells you who the subject is.

This is one of the biggest differences from English.

It can be either, depending on context.

Avisar often means:

• to inform
• to let someone know
• to warn

In this sentence, Les avisa del zumbido could be understood as:

• He/She informs them about the buzzing
• He/She warns them about the buzzing

The exact nuance depends on the situation. If the buzzing is a symptom that matters medically, warns may sound natural. If it is just giving information, informs may fit better.

Because one common structure is:

avisar a alguien de algo

This means:

• to inform/warn someone about something

So:

• les avisa del zumbido literally follows that pattern:
• [to them] [he/she informs/warns] [about the buzzing]

You may also see other constructions with avisar, but this one is very common and important to learn.

Zumbido literally means buzzing or humming.

Depending on context, especially in a medical context, it can refer to a buzzing/ringing sound in the ear.

So it may correspond to things like:

• buzzing
• ringing
• humming

The best translation depends on the context already given to the learner.

Tímpano usually means eardrum in this kind of sentence.

It can also refer to tympanum in more technical or architectural contexts, but here the medical meaning is clearly the relevant one.

So:

• evaluar el tímpano = to evaluate/examine the eardrum

Yes, especially in a technical, clinical, or medical register.

In more everyday English, you might translate it as:

• examine the eardrum
• check the eardrum

But Spanish often uses evaluar in professional or medical contexts where English might prefer assess, evaluate, or examine depending on the situation.

Yes. That is a very close literal structure.

Piece by piece:

• Les = to them
• avisa = warns / informs
• del zumbido = about/of the buzzing
• antes de que = before
• evalúen = they evaluate / you all evaluate
• el tímpano = the eardrum

A more natural English translation may vary, but grammatically that is very close to the Spanish structure.

Spanish often uses the definite article where English might or might not use it.

So el tímpano is normal Spanish for the eardrum.

In context, Spanish prefers the article with body parts much more often than English does. Even though English sometimes says the eardrum, Spanish usage with el is completely expected here.

Yes, but it changes the structure slightly.

• antes de que evalúen el tímpano = before they/you all evaluate the eardrum
• antes de evaluar el tímpano = before evaluating the eardrum / before to evaluate the eardrum (natural English: before evaluating)

The version with antes de que + subjunctive is used when there is a new subject or a clearly finite clause.
The version with antes de + infinitive is often used when the subject is the same or when Spanish prefers a more compact construction.

So both are possible in the right context, but they are not interchangeable in every situation.

Yes, it sounds somewhat formal and possibly medical/clinical, mainly because of:

• zumbido
• evaluar
• tímpano

In casual conversation, someone might choose simpler wording depending on the situation. But as written, the sentence sounds quite natural in a professional or clinical context.

Yes.

Les can mean to you all if the group is ustedes.

However, in Spain:

• vosotros is normally used for informal you all
• ustedes is more formal, or used in some regional varieties

So if this sentence is from Spain Spanish, les plus evalúen may suggest:

• a formal plural you all, or
• simply them, depending on context

That ambiguity is normal in Spanish.