Learn Hardcore Finnish: Kova ääni häiritsee minua yöllä.

Minua is the partitive form of minä. In this sentence, minua is not the subject; it is the person being affected by the action of the verb häiritsee (disturbs).

Many Finnish verbs (including häiritä) require their object or “experiencer” to be in the partitive case. So you say:

Kova ääni häiritsee minua. – A loud sound disturbs me.

Compare:

Minä häiritsen sinua. – I disturb you.
- minä = subject (nominative)
- sinua = person being disturbed (partitive)

Why does häiritsee end in -ee and not just häiritse?

The dictionary form is häiritä (to disturb). In the present tense its stem is häiritse-, and then we add personal endings:

minä häiritsen
sinä häiritset
hän häiritsee
me häiritsemme
te häiritsette
he häiritsevät

For the 3rd person singular (hän), the ending is basically -e added to häiritse-, which results in häiritsee (the two e’s in a row become a long ee).

So häiritsee is simply the regular 3rd person singular present form:
(kuka?) kova ääni häiritsee – the loud sound disturbs.

Can I change the word order to Minua häiritsee kova ääni yöllä?

Yes. Both are grammatically correct:

Kova ääni häiritsee minua yöllä. (neutral, default)
Minua häiritsee kova ääni yöllä. (emphasis on me or on the fact that I am the one disturbed)

Finnish word order is quite flexible. Usually:

The first element carries more emphasis or is the “topic” of the sentence.

So:

Kova ääni häiritsee minua yöllä. – You are stating what a loud noise does.
Minua häiritsee kova ääni yöllä. – You might be contrasting with someone else (e.g. Others sleep fine, but *I am disturbed by loud noise at night*).

Why is ääni singular when in English we might say “loud noises disturb me at night”?

Finnish often uses the singular when English uses a plural for general statements.

Kova ääni häiritsee minua yöllä.
Literally: A loud sound disturbs me at night but can be understood as a general habit, similar to Loud noise/noises disturb me at night.

If you really want to stress many separate sounds, you can use the plural:

Kovat äänet häiritsevät minua yöllä. – Loud sounds/noises disturb me at night.

But for a general sensitivity to noise, the singular kova ääni is perfectly natural.

What case is yöllä, and what does the ending -llä mean?

Yöllä is in the adessive case (ending -lla / -llä).

The basic form is yö (night).
Adessive is formed: yö → yöllä

The adessive often means:

location “on, at” (e.g. pöydällä – on the table)
time “at” (e.g. päivällä – in the daytime)

So yöllä literally is “at night” in the sense of during the night time.

Thus:

Kova ääni häiritsee minua yöllä. – A loud sound disturbs me at night.

I learned that ääni can mean “voice”. How do I know whether it means “voice” or “sound/noise” here?

Ääni has several related meanings:

voice (human voice)
sound or noise in general
even vote (in elections)

Here, with adjective kova (hard/loud), the natural interpretation is sound/noise:

kova ääni = a loud sound, loud noise
kaunis ääni = a beautiful voice (of a singer)
40 ääntä vaaleissa = 40 votes in an election

Context and the adjective around ääni tell you whether it is “voice”, “sound/noise”, or “vote”.

Why does häiritä use the partitive minua instead of minut?

Minut is the accusative form of minä, used mostly with totally affected or fully completed actions:

Hän näki minut. – He saw me.
Hän löysi minut. – He found me.

Some verbs, however, always take a partitive object regardless of completeness. Häiritä is one of these.

Kova ääni häiritsee minua. – A loud sound disturbs me.

You would not say häiritsee minut in this sense. Other verbs that typically take partitive objects include:

rakastaa minua – to love me
odottaa minua – to wait for me
auttaa minua – to help me (often partitive, though minut also appears in some styles)
pelottaa minua – to scare me

So you simply have to learn häiritä + partitive as a pattern.

Can I say öisin instead of yöllä, and what is the difference?

Yes, but the nuance changes slightly.

yöllä = at night, referring to a particular night or just night-time in general.
öisin = at nights / during nights (habitually), more clearly a repeated, habitual action.

So:

Kova ääni häiritsee minua yöllä.
– A loud sound disturbs me at night (could be one night or generally).
Kova ääni häiritsee minua öisin.
– Loud sound disturbs me at nights, i.e. it happens regularly at nights.

Both are correct; öisin makes the habitual nature more explicit.

What is the difference between kova ääni and kovaa ääntä?

The difference is both case and function:

kova ääni: nominative case
- typical subject: Kova ääni häiritsee minua. – A loud sound disturbs me.
kovaa ääntä: partitive case
- usually used as an object or with verbs of perception / existence:
  - Kuulin kovaa ääntä. – I heard a loud sound/noise.
  - Kovaa ääntä kuuluu ulkoa. – Loud noise can be heard from outside.

In this sentence, kova ääni is the subject, so it stays in the nominative.
Partitive kovaa ääntä would not be used here as the subject in a normal active sentence with a personal verb form like häiritsee.

How would I say “Loud sounds disturb me at night” in Finnish?

Use the plural form for both the adjective and the noun, and conjugate the verb in plural:

Kovat äänet häiritsevät minua yöllä.

Breakdown:

kovat – plural nominative of kova (loud)
äänet – plural nominative of ääni (sounds/noises)
häiritsevät – 3rd person plural present of häiritä
minua – partitive of minä
yöllä – at night

How do I pronounce häiritsee, especially ä and the ei part?

Pronunciation tips:

Stress is always on the first syllable: HÄI-rit-see.
ä: like the a in English “cat”, but a bit clearer and more fronted.
ei: a diphthong, roughly like the “ei” in “eight” or the “ay” in “say”.
ts: like ts in “cats”.
ee: a long e sound; hold it about twice as long as a short e.

So slowly: HÄI-rit-see → [ˈhæi̯ritseː] (approximate IPA).

Is there a difference between kova and äänekäs when talking about loud sounds?

Yes, there is a nuance:

kova = literally “hard, strong”, and by extension loud
- kova ääni – a loud sound/noise
- kova musiikki – loud music
- kova tuuli – strong wind
äänekäs = “noisy, loud” (often with a sense of a lot of noise, especially from people)
- äänekäs lapsi – a noisy child
- äänekäs ryhmä – a loud/noisy group

In your sentence, kova ääni häiritsee minua yöllä is perfectly natural.
If you said äänekäs ääni, it would sound odd; better would be äänekäs naapurusto (a noisy neighbourhood).

How do I say “A loud sound does not disturb me at night” in Finnish?

Use the negative verb ei and put the main verb into the connegative form (same as the stem used with en, et, etc.):

Kova ääni ei häiritse minua yöllä.

Structure:

Kova ääni – subject (a loud sound)
ei – 3rd person singular negative verb
häiritse – connegative form (no personal ending)
minua – partitive (me)
yöllä – at night

So the pattern is:
[subject] + ei + [verb connegative] + [partitive object] (+ time expression).