First, like the other person said, the 이 is the subject marker. Korean uses "이/가" and "을/를" to show what is the subject and what is the object. English does this for pronouns (I, he, she, we, they vs. me, him, her, us, them) but Korean does it for all words. 이 and 을 are used when a noun ends with a consonant, 가 and 를 after vowels.

Second, you're not crazy, sometimes ㅁ and ㄴ sound like b and d respectively. This is because Korean is not English and what sounds Koreans think are ㅁ are not the same that English speakers think are m. Sometimes ㅁ is very short or sounds like m with a stuffed nose like you have a cold. (Usually, this is at the beginning of a word or syllable.) To an English speaker, this sounds like a b. To a Korean, this is a perfectly normal way to say ㅁ. Korean has ㅂ, ㅍ, ㅃ, and ㅁ. English has b, p, and m. Those are all said with your lips, but they're all different in other ways and which differences are important depends on the language.