Během nočního klidu nesmí být hluk.

Během means during. It introduces the time frame for the whole sentence: during the nighttime quiet period.

In Czech, it is very common to put a time expression at the beginning of the sentence, especially when it sets the scene for everything that follows.

So:

• Během nočního klidu = during the nighttime quiet period
• nesmí být hluk = there must not be noise / noise is not allowed

The word order is natural and neutral.

Because během requires the genitive case.

So the noun klid has to change form:

• nominative: klid
• genitive: klidu

And the adjective noční must match the noun in case, gender, and number:

• nominative: noční klid
• genitive: nočního klidu

This is a very important pattern:

• během dne = during the day
• během noci = during the night
• během nočního klidu = during the nighttime quiet period

Because it is the genitive singular form of the adjective noční, agreeing with klidu.

Here the noun klid is:

• masculine
• singular
• genitive

So the adjective must match it:

• nominative masculine singular: noční klid
• genitive masculine singular: nočního klidu

For a learner, the key idea is: after během, both the adjective and noun shift into the genitive.

Literally, yes, noční klid is something like night peace / nighttime quiet. But in real Czech, it is a set phrase meaning quiet hours at night, often in rules, building notices, or laws.

So this sentence sounds like something you might see in:

• an apartment building
• hotel rules
• camping rules
• municipal regulations

It is not mainly poetic here; it is practical and official-sounding.

Because the sentence expresses prohibition, not simple description.

• nesmí být hluk = there must not be noise / noise is not allowed
• není hluk = there is no noise
• hluk není = the noise is not... or a marked version of there is no noise, depending on context

So:

• není hluk describes a situation
• nesmí být hluk gives a rule

That is a big difference.

Literally, it means something like noise must not be.

Czech often uses být in this kind of impersonal rule:

• Tady nesmí být psi. = Dogs are not allowed here.
• V místnosti nesmí být kouř. = There must not be smoke in the room.
• Během nočního klidu nesmí být hluk. = During quiet hours, there must not be noise.

This is similar to English there must not be..., even though Czech does not need a word like there in this structure.

Czech has no articles like a or the, so the noun appears by itself: hluk.

Also, here hluk is being used in a general sense, like English noise:

• Hluk je problém. = Noise is a problem.
• Nesmí být hluk. = There must not be noise.

So this is not talking about one specific sound. It means noise in general is not allowed.

Grammatically, yes, you can think of hluk as the thing whose existence is being talked about.

But the sentence is also somewhat impersonal in feel, because the main idea is a rule:

• nesmí být = must not be
• hluk = noise

So a useful English equivalent is:

• There must not be noise rather than
• Noise must not be

The second one is too literal and unnatural in English, even though it reflects the Czech structure more closely.

Because nesmí means must not / is not allowed to, while nemůže means cannot / is not able to.

Compare:

• Nesmí být hluk. = Noise is not allowed.
• Nemůže být hluk. = There cannot be noise / noise cannot exist.

The second sentence would usually mean impossibility, not a rule. In your example, the meaning is clearly prohibition, so nesmí is the correct choice.

Yes, Czech word order is flexible, but the original order is the most natural for a neutral rule or notice.

Original:

• Během nočního klidu nesmí být hluk.

Possible alternatives:

• Hluk během nočního klidu nesmí být.
• Nesmí být hluk během nočního klidu.

These are possible, but they sound more marked or place emphasis differently.

For a sign, rule, or standard statement, the original version is the best choice because it starts with the time condition and then gives the rule.

A rough pronunciation guide is:

BYE-hem NOCH-nyi-ho KLI-doo NES-mee beet hlook

A few useful notes:

• bě sounds roughly like bye with a soft b
• čn in nočního is pronounced like ch in church, followed by ny
• í is a long vowel
• hl at the start of hluk may feel unusual to English speakers, but Czech allows that cluster

A more approximate phonetic version is:

[bjeɦɛm not͡ʃɲiːɦo klɪdu nɛsmiː biːt ɦluk]

It sounds official and rule-like, but still completely normal Czech.

You would expect it in contexts like:

• house rules
• public notices
• campsite regulations
• municipal announcements

In casual speech, people might say something more direct, for example:

• V noci nedělejte hluk. = Don’t make noise at night.
• Počas nočního klidu buďte potichu. = Be quiet during quiet hours.

So your sentence is natural, but it has the tone of a regulation rather than casual conversation.