The reason why it may sound like that is because if you were to be in another Hispanic country and you heard them speak the native tongue, it will sound more like bibo replacing 'v' with a 'b' sound. Just like when you say, Montevideo, Uraguay, it sounds like "Montebideo" or "bideo" for when you say "hacer un video." I hope this helps you understand why it may sound like that.
I have heard this many times as well, and wondered the same thing. I copied this answer from SpanishDict.com answers, which seemed to give a pretty good explanation: "It all depends on the location. For example, in Medellin in Colombia, yo is pronounced jo. Actually almost any word that has a y sound (both Y's and LL's) is said like a j or something like shz. That is why there are also two ways to say Medellin: me-de-shzín / me-de-yín. The funny thing is, I have heard some Colombians ask me "Jes or no?" because they think that all y's are said like j's. (Personally, I think the sound of J in Spanish is beautiful, so I use it, but in reality it's not that hard to switch back to Y.)"
I hope this helps!
Whether you use "a" or "an" is dependent solely on whether the noun it follows starts with a consonant or a vowel. If the word starts with a vowel, it uses "an", but if the word begins with a consonant, it uses "a". There are only a few exceptions to this rule, such as certain words that begin with an "h", but the "h" is silent, such as in "an hour". The number is irrelevant, as "a" and "an" are only used to denote singular nouns.
A cat, a cats. An apartment, an apartments. Sounds wrong, doesn't it? This is because you cannot use "a" or "an" before plural nouns.