The most likely cause of what you describe is that the string is hitting the first fret because of a too-deep notch in the nut.
If you are not "techie" inclined, your best bet is probably to take it to a good guitar repair person, or at least find a more experienced player to take a look at it.
If you want to "investigate," you could loosen the problem string Just enough to slip a strip cut off something like a business card between the string and the nut, and see if it stops the noise after you retune. Use a strip a little wider than the nut. Get it in, and retune; then, if you like, clip off the ends. If it helps, the nut probably needs to be raised, although a raised fret is still a possibility.
If the nut is low, your repair person may be able to shim up the existing nut, or may want to replace it, depending on what condition it's in otherwise.
The second possibility is that the first (or second) fret has "raised" slightly at one end. A short, straight-edge like a 6" ruler that spans about 4 frets, placed along a string and pressed down on the frets should slide smoothly up and down the string. If it "hangs" when you slide it onto the first fret, then the fret may be loose, or just raised a little. A lttle bit of a "bump" as the straightedge contacts a new fret is possible, so you need to compare how it feels against the first string with the feel against the 6th. You should be able to tell if the fret is "out of place."
A raised fret can be replaced, reseated, or just filed down to where it should be - or often a combination of "all of the above." It's impossible to say, without a "hands-on-look" at your guitar, which procedure is best; so your "repairist" should tell you what's recommended.
It's also possible that the problem is not in the string/fret/nut/bridge setup. There are a surpirising number of little pieces and parts that can rattle and buzz - often only at particular frequencies, so you should look the instrument over very carefully for loose screws, separated glue lines, lumpy string windings on the tuners, excess "end-wire," and such. If you have a pickup, any loose wires (like between the pickup and battery and/or plug) are likely suspects.