I just bought the same TV last week and I also heard a faint noise while standing right at the screen. Depending on how long you've had it, take it back if it really bothers you. If it's audible from sitting down while viewing, there is definitely a problem because the only way for me to hear it is standing with my ear right at the screen. I have heard of others complaining of the buzzing noise and returning it.
Could just be a quirk of this model. It is definitely considered a low-budget model but the picture quality makes it unbeatable in that price range. If you're not happy with it, I can recommend a few replacement models for you.