All are fine. And yes, "it" is an impersonal pronoun here, more of an introductory word, just as "there" can be.
http://www.google.com/#q=impersonal+it+and+introductory+there
2. It is too noisy and we can hardly hear each other.
3. It is too noisy for the man to sleep.
4. There must be a fight going on outside. It is way too noisy.
5. Anything doing? Why is it so noisy?
6. It is too ugly and too noisy.
7. It was noisy with the sound of many voices.
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Are they all grammatical? Does 'it' refer to ambiguous environment? Is 'it' all 'an impersonal pronoun in each sentence?
http://www.google.com/#q=impersonal+it+and+introductory+there
In sentences 1, 2, 3, and 6, 'it' refers to the noisy environment or surroundings. In these sentences, 'it' acts as an impersonal pronoun referring to the general situation or condition being described.
In sentence 4, 'it' is also referring to the noisy environment, but the phrase "there must be a fight going on outside" suggests a specific cause for the noise.
In sentence 5, 'it' is an impersonal pronoun used to refer to the general situation or condition, but it is not clear what exactly the noise is referring to (e.g. whether it's from construction, a party, or some other source).
In sentence 7, 'it' refers to a specific context mentioned earlier, where there were many voices creating noise. The phrase "with the sound of many voices" clarifies the context of the noise.
So, while 'it' generally acts as an impersonal pronoun, the specific referent of 'it' can vary depending on the sentence.