Some Piyutim recited on Shabbath are widely (in the Ashkenazi world) sung by the congregation (usually in unison, but in some rare instances in the Ashkenazi world they are sung responsively). Among them, and I don't mean to leave any out, are Lecha Dodi on Friday night, Kel Adon in Birchoth Keriath Shema', and Ein KeLokeinu.
However, some, primarily (in my perception) Yeshivish congregations (and Yeshivoth) don't sing them, but rather recite them quietly. Sometimes the Ḥazzan will sing it and the congregation will recite it quietly after (or sometimes before) him.
Why the discrepancy?