Τρομάζω όταν ακούω δυνατό χτύπο στην πόρτα αργά τη νύχτα.

Because Greek usually leaves out subject pronouns when the verb ending already shows the person.

Here, τρομάζω clearly means I get scared / I am frightened, so εγώ is unnecessary unless you want emphasis.

• Τρομάζω = I get scared
• Εγώ τρομάζω = I get scared, with extra emphasis

Yes. Τρομάζω can be either:

• intransitive: I get scared / I am startled
• transitive: I frighten someone

In this sentence it is intransitive, because there is no object after it. So it means:

• I get scared
• I am startled

Compare:

• Τρομάζω όταν ακούω... = I get scared when I hear...
• Τρομάζω το παιδί. = I frighten the child.

The present tense here expresses a general or repeated situation, not just one specific moment.

So the sentence means something like:

• I get scared whenever I hear a loud knock on the door late at night.

This is a common use of the Greek present, just like the English present in sentences such as:

• I get nervous when people shout.
• I wake up early when I’m stressed.

Because όταν ακούω suggests a habitual / repeated meaning: whenever I hear.

• όταν ακούω = when/whenever I hear, in general
• όταν ακούσω = when I hear, referring more to a single future occasion

So:

• Τρομάζω όταν ακούω... = I get scared whenever I hear...
• Θα τρομάξω όταν ακούσω... = I will get scared when I hear...

This is a very common contrast in Greek.

Because χτύπο is the direct object of ακούω, so it must be in the accusative case.

Dictionary form:

• ο δυνατός χτύπος = the loud knock / bang

In the sentence:

• ακούω δυνατό χτύπο = I hear a loud knock

Both the noun and adjective change to match the accusative singular masculine:

• nominative: δυνατός χτύπος
• accusative: δυνατό χτύπο

Greek often leaves out the indefinite article in cases like this.

So:

• ακούω δυνατό χτύπο = I hear a loud knock

is perfectly natural.

You could also say:

• ακούω έναν δυνατό χτύπο

That would also mean I hear a loud knock, but with a slightly more explicit one / a certain feeling.

In many everyday sentences, Greek simply omits έναν / μια / ένα where English uses a/an.

It can mean either, depending on context.

The noun χτύπος has a broad meaning related to:

• hit
• strike
• knock
• bang
• thud
• sound of impact

Because the sentence says στην πόρτα, the natural interpretation is:

• a knock on the door
• or a bang on the door

The adjective δυνατό makes it sound strong or loud, so loud knock or hard bang are both possible translations.

Στην is the contraction of:

• σε + την = στην

The preposition σε is very common and takes the accusative in Modern Greek.

So:

• στην πόρτα = at/on the door

In this sentence, it goes naturally with χτύπο:

• χτύπο στην πόρτα = a knock on the door

This is just the normal Greek way to express that idea.

Because this is a very natural Greek time expression meaning:

• late at night

It is made of:

• αργά = late
• τη νύχτα = at night

So together:

• αργά τη νύχτα = late at night

Greek often uses this kind of structure for time expressions. It does not need a preposition like English at.

Both can exist, but τη νύχτα is very common in standard everyday Greek.

The final -ν of την is often dropped before many consonants, and that is why you often see:

• τη νύχτα
• τη μέρα
• τη φορά

Some speakers and styles keep την more often, but τη νύχτα is completely normal.

The word order is not completely fixed. Greek is more flexible than English.

The given sentence sounds natural and neutral:

• Τρομάζω όταν ακούω δυνατό χτύπο στην πόρτα αργά τη νύχτα.

But you could move parts around for emphasis, for example:

• Τρομάζω αργά τη νύχτα όταν ακούω δυνατό χτύπο στην πόρτα.
• Όταν ακούω δυνατό χτύπο στην πόρτα αργά τη νύχτα, τρομάζω.

These versions still mean basically the same thing, but the focus or rhythm changes slightly.