"Why is it so noisy here?"
Translation:Почему здесь так шумно?
Loud and noisy have similar but slightly different meanings in English. For example...Loud music pertains to the VOLUME of the music being played. Noisy music pertains to the QUALITY of the music being played. Another example...A loud voice can be heard better than a soft voice, whereas a noisy voice can be distinguished or recognized from a monotone voice.
так is adverb in this sentence and means 'so', can't be inflected.
такой and такая (and такое for neutral) are adjectival pronouns and they are usually mean: as, similar, like. Example: he is like everybody - он такой как все. Sometimes they can be used as a sort of amplification of the quality similarly to English 'so' (might be confusing with the first one). Examples: she is so smart - она такая умная. the car is so expensive - эта машина такая дорогая (there are no articles in Russian, so for the definitive article you may use этот (m), эта (f), это (n))
I think the point is that 'noisy' in this phrase is not a modifier to a noun:
почему здесь так шумно : why is it so noisy here?
'so noisy' is predicate, 'noisy' is definitely not describing a noun. (You cannot say 'a noisy it'. )
он так громко дышит: He is breathing so loudly
Same goes for 'громко', it does not describe a noun, but instead how he breathes.
почему ты слушаешь такую шумную музыку : why do you listen to such noisy music? 'noisy' is adjective to the noun 'music', and 'such' (такая -> такую) takes on its female accusative form to fit with 'noisy music', which you can say, as opposed to 'noisy it'.
I am not a native Russian speaker, if this is wrong don't hesitate to correct me.
Sorry, but I think this is all wrong. 'noisy' is always an adjective. 'so noisy'is predicative, but predicative words can still be adjectives.
If you think that шумно is not an adjective here then it would have to be an adverb, in which case the literal translation would be to use 'noisily' instead. Since that doesn't make sense, it suggests to me that the шумно is behaving like an adjective.