This is the 17778th most frequent Korean word.
소음이
"소음이" means "noise" in English.
In this sentence, '소음이' refers to the subject of the sentence, which is 'noise', specifically describing its size (loudness) as an obstacle to concentration.
소음이 너무 크면 집중하기 어려워요.
If the noise is too loud, it's hard to concentrate.
Here, '소음이' is again the subject and it implies the source of the disturbance that is being audibly perceived during nighttime.
매일 밤 소음이 귀에 들려요.
Every night, the noise reaches my ears.
In this case, '소음이' denotes the thing that undergoes a change or reduction, marking it as the focal point of the anticipated event.