Singing During Chazaras Hashatz

Question

I came across a halacha in the Mishnah Berurah (124:4:16) that teaches certain behavior of the congregation during the repetition of the Shemonah Esrei. Everyone who is present in shul must be silent, listen to the brachos the chazzan is saying, and answer amein. The Mishnah Berurah adds that one should refrain from calling aloud and joining the chazzan’s tune for a few words, because it is considered arrogant and frivolous behavior.

Does the same halacha apply on Shabbos and Yom Tov, when it is common for some people to join the chazzan’s tune at certain junctures, such as during Shabbos Mincha at “tiferes gedulah va’ateres yeshuah” or during Mussaf on Yom Tov at “bechag hamatzos, uvechag hashovuos”? I find that this joint humming makes the davening nicer. Must I be careful not to do this anymore?

Thank you,

 Yehoshua, Kiryat Sefer

Rav Auerbach 

When it became a type of minhag to join the chazzan at certain places, and it is done to awaken the attention of the congregation to the tefillah, it is not called arrogant and frivolous.