Пол скрипит, когда я иду по коридору ночью.

Пол is the subject of the sentence, so it stays in the nominative case.

• пол = floor (subject form)
• пола would usually be genitive singular, which would not fit here

In Пол скрипит, the structure is simply:

• пол = the floor
• скрипит = squeaks / creaks

So literally: The floor squeaks.

Скрипит is the 3rd person singular present tense of скрипеть.

So:

• скрипеть = to creak / squeak
• скрипит = it creaks / squeaks

It matches пол, which is singular. Russian often uses the present tense for things that happen regularly or characteristically, just like English:

• Пол скрипит = The floor squeaks / creaks

Because когда я иду по коридору ночью is a subordinate clause.

Russian normally puts a comma before conjunctions like когда when they introduce a dependent clause:

• Пол скрипит, когда я иду по коридору ночью.

This is very standard Russian punctuation.

Когда means when, while если means if.

Here the sentence describes what happens when the speaker walks down the corridor at night. It is not uncertain or hypothetical in the same way if would be.

• когда = when
• если = if

So this sentence means the floor squeaks when I walk down the corridor at night, not if I walk down the corridor at night.

This is a very common question because Russian has two common verbs for to go on foot:

• идти → иду = to be going, moving in one direction, a specific instance
• ходить → хожу = to go habitually, repeatedly, or in various directions

In this sentence, иду fits because it presents the action as a particular movement through the corridor:

• когда я иду по коридору ночью = when I am walking / when I walk down the corridor at night

If you said когда я хожу по коридору ночью, it would sound more like a repeated or habitual activity: when I walk around the corridor at night / when I go along the corridor at night regularly.

So иду is the more natural choice here.

After по in this meaning, Russian often uses the dative case to express movement along, down, or through an area.

• коридор = corridor
• по коридору = along/down the corridor

The dative singular form of коридор is коридору.

So:

• иду по коридору = I walk/go down the corridor

This is a very common pattern:

• идти по улице = to walk along the street
• гулять по парку = to walk around the park
• ехать по мосту = to drive across/along the bridge

Usually it means down the corridor, along the corridor, or through the corridor, not just simple location.

Compare:

• в коридоре = in the corridor
• по коридору = along/down the corridor

So in this sentence, the idea is movement through that space, not just being located there.

Ночью is the instrumental case of ночь, and it is very commonly used as an adverb meaning at night.

So:

• ночь = night
• ночью = at night

This is a fixed, very common pattern in Russian for parts of the day or time expressions:

• утром = in the morning
• днём = in the daytime / during the day
• вечером = in the evening
• ночью = at night

So ночью is exactly the natural form here.

Russian has no articles like a or the.

So пол can mean:

• a floor
• the floor

and коридор can mean:

• a corridor
• the corridor

The exact meaning depends on context. In this sentence, English naturally uses the because the speaker presumably means a specific floor and corridor, but Russian does not need separate words for that.

Yes. Russian word order is fairly flexible, although the original version sounds natural and neutral:

• Пол скрипит, когда я иду по коридору ночью.

You could also say:

• Когда я иду по коридору ночью, пол скрипит.

That puts a little more focus on the when clause first. The basic meaning stays the same.

Russian often changes word order for emphasis, rhythm, or style, but not all orders sound equally natural in every context.

Usually it suggests a general or repeated action: the floor creaks/squeaks as the speaker walks.

So the sentence does not mean just one single squeak. It gives the idea that this is what the floor does during that situation.

Russian present tense often works this way, just like English:

• Собака лает, когда кто-то приходит. = The dog barks when someone comes.
• Пол скрипит, когда я иду по коридору ночью. = The floor squeaks when I walk down the corridor at night.

The main stresses are:

• пол
• скрипи́т
• когда́
• иду́
• по коридо́ру
• но́чью

So a natural pronunciation would be:

Пол скрипи́т, когда́ я иду́ по коридо́ру но́чью.

Stress is important in Russian, because it is not always predictable.

Yes. In context, both can work in English.

• when I walk down the corridor at night
• when I am walking down the corridor at night

Russian present tense does not always match exactly one English tense form. Here иду can suggest an action in progress or a typical event in that situation. English chooses between walk and am walking depending on style and context.

It is neutral and completely natural in everyday Russian. Nothing in it is especially formal, literary, or slangy.

A native speaker could easily say this in normal conversation or write it in a simple narrative.