That's just your good hearing and a tonal variation in pronunciation. But, it's also about stressing a particular word. In this case,
/eːn/ (stressed) is "eaaan" and
/ən/ (unstressed) is "ennn".
Furthermore, if you see én, that's actually the cardinal number one (1) which obviously uses the stressed version.
Nouns of feminine gender ( ei jente, ei kvinne ) in Norwegian can take the masculine form of the indefinite article ( en jente, en kvinne ) and still be grammatically correct.
Their usage typically depends on the dialect a particular person is speaking in. More importantly, it's a good idea not to mix them while talking or writing (for example, using ei kvinne in the first sentence and then en kvinne in the second one).
P.S. RajaReddyTKM asked the same question so next time around, please read all posts on the discussion page before asking similar questions.
Our mind reader apparatus is being serviced so we currently lack this functionality when providing answers. We do apologise for this inconvenience and in the meantime, you will have to transfer your thoughts using the old-fashioned way (words) in order to get help.