Should seeking forgiveness be secret or public, and must it be accompanied by a whistling sound?

It is better for seeking forgiveness (Istighfar) to be discreet because it is closer to sincerity and further from conceit and showing off. This is unless there is a benefit that necessitates vocalizing it, such as hoping for others to emulate it or to ward off sleep and laziness. The whistling sound present when pronouncing the letter 'seen' should not be audible.