R Shlomah Zalman Auerbach Held That the Recital of Vayechulu In the Silent Shemonah Esrei Is Considered with The Tzibbur

R’ Shlomah Zalman held that strictly speaking “Vayechulu” recited in the silent shemonah esrei is enough. Although not everyone says it at the same time (as when one person is up to “Vayechulu” another is up to “Retezei”), since it is not proper eidus, as we find that a father and son can say it together, rather, it is just a minhag and slightly comparable to eidus, it is good enough (Halichos Shlomah – Hilchos Tefillah, Perek 14, Devar Halachah s.k. 9)

If One Is Up to “Vayechulu” In His Silent Shemonah Esrei, May He Say “Vayechulu” Out Loud Together With the Tzibbur?

If one davens shemonah esrei very slowly on Friday night (or he comes late), and by the time he gets to “Vayechulu” the tzibbur is already up to saying “Vayechulu” out loud, can he join in and say “Vayechulu” out loud, or is it forbidden for one to raise his voice during his silent shemonah esrei, and he should carry on quietly and say it with someone after he finishes shemonah esrei?