A pronuncation question concerning ない

When I first started learning Japanese, I always heard ない being pronounced nai, rhyming with the English word high. Recently, however, I'm starting to hear variations on the pronunciation of ない. One was ない prounced like "nah-ee", rhyming with the English word knee. Another was ない pronounced like "neh," rhyming with the English word "heh." I'm wondering the following:

1. Is this some sort of regional variation? I tried looking it up on Wikipedia, but that was no help.
2. Is this nonstandard Japanese?
3. Is this something related to politeness?
I'm confused here...

it's common for sounds to get distorted, especially the あい at the end of words. In very casual speech, guys will often change it to a long えい.

They're just variations that communicate different emotions and attitudes. Think of all the different ways we say something like 'No way' in English. It seems like there is no difference but we extend and pronounce the vowel differently depending on how strong or casual or humourous the intention behind it is. That varies by age, gender, topic, situation, etc. To us, the focus is more on the words, and the pronunciation is processed maybe subconsciously or a little less intensely because we're accustomed to hearing it as native speakers.

To someone learning another language their level of listening comprehension is different. Aside from being a little less developed, they're trying to take everything in bit by bit and process it very carefully. It's as Noam Chomsky suggested, language is instinctual. If our brains are on high alert and processing very intensely because we really want to understand it and we've placed a false sense of importance on it, the minor variations cause trouble because we are worried about them instead of the big picture.

Personally I've found it beneficial to just 'sit back' in my head and 'take it all in' when listening to a native speaker of Japanese. I fear my listening comprehension would be much worse than it already is if I didn't do that. (> <

I fully agree with bakaKanadajin.

有り難うでございます.

Admittedly I have been studying this for only about two years now, and I haven't spent the requisite 5 years in Japan to become familar with the language.

requisite 5 years in Japan?