Learn Finnish: Yhtäkkiä kellarista kuuluu aavemaista kuiskailua. - Suddenly, ghostly whispering is heard from the basement.

This sentence uses an existential clause structure, which typically follows a Location + Verb + Subject word order. The location (kellarista) comes first to set the scene, followed by the verb (kuuluu), and finally the new subject being introduced (aavemaista kuiskailua).

Why is "aavemaista kuiskailua" in the partitive case here?

In existential clauses, the subject is in the partitive if it is an uncountable noun or an undefined plural. Because kuiskailu (whispering) is an uncountable, continuous phenomenon appearing in the scene, both the noun and its adjective aavemainen take the partitive.

The English translation says "is heard", so why isn't the Finnish verb in the passive voice?

Verbs of sensory perception like kuulua (to be heard), näkyä (to be seen), and tuoksua (to smell) are actually active verbs in Finnish. They describe how something presents itself to the senses. They are frequently used in dynamic existential clauses and naturally take the 3rd person singular form.

How is the noun "kuiskailu" formed?

It is built from the base verb kuiskata (to whisper). Adding a frequentative suffix gives kuiskailla (to whisper repeatedly or continuously), and adding a noun-forming suffix creates kuiskailu (the act of continuous whispering).