souon ga sinpai nara, yoru ni mou itido kite kakuninsitara dou?

Because 心配 is being used here as an adjective-like word, not as the verb 心配する.

• 騒音が心配 = I’m worried about the noise / noise is a concern
• 騒音を心配する = to worry about the noise

With 心配 used this way, the thing that causes concern is often marked by が.

Compare:

• お金が心配です。 = I’m worried about money.
• 将来が心配です。 = I’m worried about the future.

So 騒音が心配なら is very natural.

心配 is a na-adjective (and also a noun, depending on how it is used).

In this sentence, it works like a predicate meaning worried / concerned:

• 騒音が心配だ = I’m worried about the noise

Then it becomes:

• 騒音が心配なら = if you’re worried about the noise

So even though English uses a verb like worry, Japanese often uses 心配 as an adjective-like expression.

Because なら attaches directly to the noun or na-adjective stem, not to だ.

So:

• 静かだ → 静かなら
• 心配だ → 心配なら
• 学生だ → 学生なら

That is just how this conditional form works. So 心配だなら is not correct.

なら often means if that is the case or if you say that... It frequently responds to something already mentioned or assumed.

So 騒音が心配なら has a nuance like:

• If noise is what you’re worried about, ...
• If that’s your concern, ...

It sounds like the speaker is reacting to the listener’s concern and then offering advice.

This is a little different from a plain factual if. It feels more like given that concern, here’s what you could do.

Here に marks a point in time:

• 夜に = at night / in the evening

Japanese often uses に with specific or semi-specific times:

• 3時に
• 月曜日に
• 夜に

So 夜にもう一度来て means come again at night.

Yes. 夜 is a fairly broad word.

Depending on context, it can mean:

• evening
• night
• at night

So the exact English wording depends on the situation. If someone is checking for possible noise problems, at night is often the most natural translation, but in the evening might also fit in some contexts.

もう一度 means once more / one more time / again.

It implies that the person has already been there once before. So the sentence suggests:

• they already visited earlier
• but if noise is a concern, they should come back again at night and check

So もう一度 is an important clue to the situation.

来て is the te-form of 来る, and it links actions together.

So:

• 来て確認したらどう？
• literally: come and check—how about that?

The sequence is:

1. come
2. check

The て-form often connects actions like this in Japanese.

This depends on viewpoint.

Japanese chooses 来る or 行く based on where the speaker mentally places the center of the action.

Here, 来て suggests movement toward the place that matters in the conversation, often:

• where the speaker is
• or the place being discussed as the reference point

In English, this distinction is often less strict, but in Japanese it matters more.

So 来て here is natural if the speaker is thinking of the destination as here / this place.

Japanese often leaves obvious information unstated.

Here, the object of 確認する is omitted because it is understood from context. The speaker means something like:

• confirm whether the noise is a problem
• confirm how noisy it is at night
• confirm the situation at night

So even though Japanese does not spell it out, the meaning is clear from 騒音が心配なら.

～たらどう？ is a common way to make a suggestion.

Literally, it is like:

• How about if you check?
• Why don’t you check?

So:

• 確認したらどう？ = Why don’t you check?

This is a very natural conversational pattern.

Related forms:

• 確認したらどうですか。 = more polite
• 確認してみたらどうですか。 = softer, like why not try checking?

Yes, it is fairly casual.

Clues:

• 確認したらどう？ ends with plain どう？
• there is no です / ます
• the wording sounds like spoken advice

A more polite version would be:

• 騒音が心配なら、夜にもう一度来て確認したらどうですか。

And a slightly softer version could be:

• 騒音が心配なら、夜にもう一度来て確認してみたらどうですか。

Because Japanese very often omits subjects when they are clear from context.

In English, you usually need something like:

• If you’re worried about the noise, why don’t you come again at night and check?

In Japanese, the you is understood. The speaker is clearly addressing someone and giving advice, so there is no need to say あなたは.

In fact, explicitly saying あなた too often can sound unnatural in Japanese conversation.