1) The Gemara (Brachos 9b) tells us that one should connect Geulah to Shemoneh Esrei. Therefore, during Shachris we recite the bracha of Guol Yisrael [גאל ישראל] (Geulah) immediately prior to Shemoneh Esrei. One may not speak or even wait any amount of time between the bracha and Shemoneh Esrei. (M.B. 111:2)
2) There is a debate whether one (who is about to begin Shemoneh Esrei) may respond amen to the chazzan when he recites the bracha of Guol Yisrael. According to the Shulchan Aruch (66:7) one may not respond amen. While according to the Rama one may respond Amen. The Mishnah Berurah suggests that one should conclude the bracha with the chazzan in order to avoid reciting Amen according to all opinions. In addition, one can quickly begin Shemoneh Esrei while the chazzan is concluding the bracha in order to avoid answering Amen.
3) Many chazzanim conclude the the bracha of Guol Yisroel quietly so the the congregation cannot hear the end of the bracha and would therefore not answer Amen according to all authorities. There were rabbanim, including the Yesodei Yeshurun (vol. 1 page 284) and Harav Chaim Kanievsky shlit”a (Halichos Chaim page 38, Sheilas Rav page 212 and Ishei Yisroel 52) who endorsed this custom. However, Harav Yaakov Kamanetzky zt”l (Emes L’Yaakov page 43), Harav Shlomo Zalman Auerbach zt”l (Halichos Shlomo 7:18) and Harav Yosef Eliyahu Henkin zt”l (Gvuros Eliyahu 15, 19, 20) reject this custom and they rule that the bracha should be said out loud.