The pasuk at the beginning of the parsha of bikurim says וענית ואמרת (Hebrew- very cool, right?) “And you will anwser and say”. Rashi comments that the phrase “And you will answer” instructs the person to declare his piece out loud.
The Chanukas Habayis HaChadash asks, why does he have to say it in a loud voice? Secondly, the Gemara in Brachos says that one who utters a tefilla out loud lacks proper faith in Hashem because it appears that he is intimating Hashem can only hear a loud prayer, which is false, of course, because we know Hashem can track our deepest thoughts. Based on this, how can the person bringing the Bikurim say his Vidui out loud?
He answers based on the text which the person says. It describes how Lavan wished to destroy Yaakov Avinu and how Hashem foiled his plans. Now, Lavan never said out loud what he was going to do, so Hashem must have been able to tell what he was thinking. We also know that Hashem punishes Rishayim even for their malicious thoughts, as opposed to non-Rishayim, and that is how Lavan was destroyed.
Since this fact is being brought up, we have no reason to disallow a loud vidui, because his story about Lavan shows us that he does not believe that Hashem is limited to out-loud prayers.
Still, he does not answer the first question, why it must be out loud. A possible answer could be that a loud prayer brings with it powerful feelings. We want the ‘bringer’ to internalize the message that he has a lot to be thankful for. If anyone has another answer, please let me know.
שבת שלום משעלבים, יעקב.