Is whispered a noun

No, the Word 'whispered' is a verb, the past participle, past tense of the verb to 'whisper'. The past participle of the verb also functions as an adjective.

The Word 'whisper' is both a verb and a noun.

The noun 'whisper' is a Word for Words spoken softly and privately; a Word for a thing.

Example uses:

Jane whispered the man's name I'd forgotten into my ear. (verb)

I heard whispered rumors that their marriage is in trouble. (adjective)

You can hear the breeze whisper in the trees. (verb)

There's not a whisper of news about the new CEO. (noun)