Turns out the one spreading the rumors was Hashimoto, who did so at the behest of Sakayanagi. Shortly thereafter, Sakayanagi appears before Class C and she informs them she has evidence regarding the rumors about Ichinose.
We've been made aware of
أصبحنا محيطين علماً
Unter euch im ersten Jahr
Nous avons pu constater
Siamo al corrente
Sabemos dos comentários maldosos que estão sendo 
perpetuados entre vocês, alunos do primeiro ano.
Нам стало известно,