Learn Hardcore German: Die Bewohnerin im Erdgeschoss meint, der Komiker im dritten Stockwerk mache zu viel Lärm. - The female resident on the ground floor thinks the comedian on the third floor makes too much noise.

Bewohner is the masculine (or generic) form meaning male resident or resident in general.
Bewohnerin is the explicitly feminine form meaning female resident.

The suffix -in is the usual way to form feminine nouns from masculine ones in German:

Lehrer → Lehrerin (male teacher → female teacher)
Bewohner → Bewohnerin (male resident → female resident)

So the sentence specifies that the person on the ground floor is a woman.

Why die Bewohnerin and not der Bewohnerin?

Die Bewohnerin is in the nominative case, because it is the subject of the verb meint.

Wer meint etwas? – Die Bewohnerin.
(Who thinks/says something? – The resident.)

For a feminine noun like Bewohnerin:

Nominative singular: die Bewohnerin (subject)
Accusative singular: die Bewohnerin
Dative singular: der Bewohnerin
Genitive singular: der Bewohnerin

So der Bewohnerin would be dative or genitive, not nominative. Here we need nominative, so it must be die Bewohnerin.

What exactly is im Erdgeschoss? What does im mean?

Im is a contraction of in dem:

in
- dem Erdgeschoss → im Erdgeschoss

In with the dative case is used to talk about location (where something is):

im Erdgeschoss = in the ground floor (i.e. on the ground floor)
im Haus = in the house
im dritten Stock = on the third floor

Erdgeschoss is a noun (hence the capital letter), literally ground floor. So grammatically im Erdgeschoss is:

preposition in
dative definite article dem (merged into im)
noun Erdgeschoss in the dative

Why is there a comma before der Komiker im dritten Stockwerk mache zu viel Lärm? What kind of clause is that?

The comma separates the main clause from a subordinate (dependent) clause:

Main clause: Die Bewohnerin im Erdgeschoss meint, …
Subordinate clause: … der Komiker im dritten Stockwerk mache zu viel Lärm.

This subordinate clause gives the content of what she thinks/says. It’s a form of indirect speech (reported speech). German normally marks this in two ways:

With a comma to separate the clauses.
With subordinate clause word order (main verb at the end) and often the subjunctive (Konjunktiv I).

So the second part is not an independent statement by the narrator; it’s what the resident claims.

Why is it mache and not macht in der Komiker … mache zu viel Lärm?

Mache here is Konjunktiv I (Subjunctive I) of machen, third person singular.

Indicative (normal): er macht (he makes / is making)
Konjunktiv I: er mache

Konjunktiv I is often used in German to report what someone else says, thinks, or claims, especially in more formal language or writing:

Sie sagt, er sei krank. (She says he is ill.)
Er meint, sie komme später. (He thinks she is coming later.)

In your sentence, mache signals that this is the resident’s opinion, not a fact asserted by the narrator:

Die Bewohnerin … meint, der Komiker … mache zu viel Lärm.
= The resident thinks/claims that the comedian makes too much noise.

In everyday spoken German, many people would simply use the indicative macht (often with dass), but the version with mache sounds more written or formal.

Can we also say Die Bewohnerin im Erdgeschoss meint, dass der Komiker im dritten Stockwerk zu viel Lärm macht? Is that different?

Yes, that is perfectly correct and very common:

Die Bewohnerin im Erdgeschoss meint, dass der Komiker im dritten Stockwerk zu viel Lärm macht.

Differences:

With dass + macht
- Most common in everyday speech.
- Grammatically simple: just a normal dass-clause with the verb at the end in the indicative (macht).
Without dass + mache (Konjunktiv I)
- More typical of written style, news reports, or slightly more formal language.
- Emphasizes that this is reported speech or someone’s opinion.

In most everyday contexts, the difference in meaning is very small. Both versions express that this is the resident’s opinion, not necessarily an objective fact.

In der Komiker im dritten Stockwerk mache zu viel Lärm, why is the verb at the end?

German subordinate clauses usually put the finite verb at the end. Your clause is the content clause of meinen and follows subordinate clause word order:

Subject: der Komiker im dritten Stockwerk
Object phrase: zu viel Lärm
Finite verb at the end: mache

So the standard pattern is:

…, dass der Komiker im dritten Stockwerk zu viel Lärm macht.
Or (as in your sentence, with Konjunktiv I and no dass):
…, der Komiker im dritten Stockwerk mache zu viel Lärm.

In contrast, main clauses in German normally have the finite verb in second position:

Der Komiker macht zu viel Lärm.
Im dritten Stockwerk macht der Komiker zu viel Lärm.

What case is der Komiker, and why is it der and not den or dem?

Der Komiker is in the nominative case, because it is the subject of the subordinate clause:

Wer macht (angeblich) zu viel Lärm? – Der Komiker.

For masculine nouns:

Nominative singular: der Komiker (subject)
Accusative singular: den Komiker (direct object)
Dative singular: dem Komiker (indirect object)

Since der Komiker is doing the action of Lärm machen, it must be nominative, hence der.

Why is it im dritten Stockwerk and not im dritte Stockwerk?

Dritten is the ordinal number dritte (third) with the correct adjective ending for the dative case.

Breakdown:

im = in dem → preposition in
- dative article dem
Stockwerk is neuter: das Stockwerk
in with a static location takes the dative: in dem Stockwerk
After a definite article in the dative singular, adjectives (including ordinals) take -en:
- in dem dritten Stockwerk → im dritten Stockwerk

So:

richtig (correct): im dritten Stockwerk
falsch (incorrect): im dritte Stockwerk

Is there a difference between Stockwerk, Stock, and Etage?

All three can mean floor or storey of a building:

das Stockwerk – floor / storey (quite neutral)
der Stock – floor; very common in everyday speech (im dritten Stock)
die Etage – floor / storey (slightly more formal or used in certain regions)

Your sentence uses im dritten Stockwerk, but you could also say:

im dritten Stock
in der dritten Etage

One extra cultural point: In German-speaking countries, Erdgeschoss (ground floor) is usually the level at street level, and der erste Stock is the next floor up. That matches British usage (ground floor / first floor) and differs from American usage (first floor = ground level).

Why is Lärm capitalized, and what does Lärm machen mean?

Lärm is capitalized because all nouns in German are capitalized, regardless of position in the sentence.

Lärm is a noun meaning noise (specifically, noisy, disturbing sound). The verb phrase Lärm machen is an idiomatic expression meaning:

to make noise
to be noisy

Examples:

Die Kinder machen viel Lärm. – The children are making a lot of noise.
Der Komiker macht zu viel Lärm. – The comedian makes too much noise.

You would normally use machen, not tun, with Lärm.

Why do we say zu viel Lärm and not zu vielen Lärm?

Viel behaves differently depending on what it modifies:

With uncountable (mass) nouns in the singular and without an article, it usually has no ending:
- viel Wasser – a lot of water
- viel Lärm – a lot of noise
- zu viel Lärm – too much noise
Here Lärm is an uncountable noun, and zu viel means an excessive amount. So:
- zu viel Lärm = too much noise (correct)
- zu vielen Lärm would sound wrong in this context.
With plural nouns or in some other structures, viel can take endings:
- zu viele Leute – too many people (nominative/accusative plural)
- mit vielen Leuten – with many people (dative plural)

So zu viel Lärm is the normal, idiomatic expression for too much noise.

What is the nuance of meinen compared to denken or glauben?

All three can be translated as to think or to believe in English, but there are differences:

meinen
- “to be of the opinion”, “to hold the view that …”
- Often used when expressing an opinion or judgment.
- In your sentence, meint signals that this is simply the resident’s opinion.
denken
- General “to think” (mental activity) or “to have a thought”.
- More about the process of thinking than a stated opinion.
glauben
- “to believe” (to be convinced of something, sometimes without proof).
- Can sound stronger or more personal than meinen.

Compare:

Ich meine, der Komiker macht zu viel Lärm.
= In my opinion, the comedian makes too much noise.
Ich denke, der Komiker macht zu viel Lärm.
= I think the comedian makes too much noise (very similar in everyday speech).
Ich glaube, der Komiker macht zu viel Lärm.
= I believe / I have the impression the comedian makes too much noise.

In your sentence, meint emphasizes that this is her opinion about the situation.