Is it permissible to use a doorknocker to knock on somebody’s door on Shabbat?
The Rama (Rabbi Moshe Isserles, Poland, 1525-1572), in his glosses to the Shulhan Aruch, rules that one may not knock with a doorknocker on Shabbat, because of the prohibition against producing sounds on Shabbat. The Sages enacted a provision forbidding making sounds, as a safeguard against the possibility that someone might prepare or fix an instrument, in violation of Shabbat. According to the Rama, this would apply even to knocking with a doorknocker, and this is the Halacha for Ashkenazim.
However, Hacham Ovadia Yosef infers from the comments of the Bet Yosef (work by Maran, author of the Shulhan Aruch) that the prohibition applies only to producing sounds in a beat or rhythm. Hacham Ovadia therefore rules that for Sepharadim, one may knock with a doorknocker on Shabbat, on the condition that he does not knock to any particular beat. Sometimes, people like to make a kind of “tune” with their knocking; this would certainly be forbidden on Shabbat. But knocking indiscriminately would certainly be allowed, as such knocking is not included in the Rabbinic prohibition against making musical sounds.
These same guidelines would apply to other kinds of sounds, such as clapping and banging. It is forbidden on Shabbat to clap or bang on a table in a particular rhythm, but one may clap or bang for the sake of making noise, such as to wake somebody, or if a Rabbi bangs in the synagogue to silence the congregation. By the same token, knocking silverware against a glass in a beat or rhythm is forbidden, but one may knock indiscriminately to get a crowd’s attention. So long as the noise is not made to a specific beat, it is permissible.
The Halachic authorities rule that whistling was not included at all in the decree against producing sounds on Shabbat, and one may thus whistle a tune on Shabbat. We should note that irrespective of the laws of Shabbat, whistling in public, such as while walking in the street, is improper and unbecoming of a Torah Jew. But if at home one wishes to whistle as background to the singing of Pizmonim (hymns) at the Shabbat table, this is certainly acceptable and permissible.
Summary: One may not clap, knock on a door, bang on a table, or clank silverware to a beat or rhythm on Shabbat. One may, however, make indiscriminate noise in such a fashion, such as knocking on a door (even with a doorknocker) or clapping or banging to get a group’s attention. Whistling is permissible on Shabbat, even to a melody, though in general it is inappropriate to whistle in public, even during the week.