Does the prayer become invalid by the emission of two unintelligible letters that were not heard by those next to me?

The jurists are in agreement that prayer is nullified by speech, based on the hadiths of Zayd ibn Arqam and Mu'awiyah ibn al-Hakam al-Sulami. The majority of jurists (Hanafis, Shafi'is, and Hanbalis) hold that the speech which invalidates prayer is that from which two or more letters are formed. As for the Malikis, they hold that it is a single letter or an unmeaning sound. The Hanafis did not differentiate in the nullification of prayer by speech, whether the worshipper was forgetful, asleep, ignorant, mistaken, or compelled, with the exception of greeting (saying salām) forgetfully to exit the prayer, thinking it was completed. The Shafi'is hold that prayer is not nullified by the speech of one who forgets, or one who is ignorant of the prohibition if he is newly converted to Islam or grew up far from scholars, or one whose tongue slipped, provided the speech is minor according to custom. They cite the hadith of Dhul-Yadayn as evidence. As for one who is compelled to speak, his prayer is nullified according to the more evident opinion, even if his speech was minor; if it was extensive, it is certainly nullified. The Hanbalis hold that prayer is nullified by the speech of one who forgets and one who is compelled, and by speech for the benefit of the prayer, and by speech to warn someone like a blind person. However, prayer is not nullified according to them by the speech of a sleeper if the sleep is light, or if the speech slips from his tongue while reciting.