Weird Fret Buzz. (Apparently not lack of humidity).

Hey y'all. I have a problem with my Alhambra Maestro 200 Electric, classical guitar. (No truss rod!)

It's kind of like a double-sound buzzing that comes from mainly the D string from 1st to 6-7th fret. It's extremely annoying and very noticable. I've also tried raising the bridge some millimeters, but without success. There's also a bit of buzzing from the A and E, but nowhere near the same amount as the D.

It started suddenly while I was playing on it around a month ago. I searched the web, and came to the conclusion that it had to be caused by a lack of humidity, so I tried humidifying it for a month, and I tried yesterday to see if it had helped, but it hadn't.

The weird thing about it is that it's only if I hold down the string in the middle of two frets, if I place my finger just next to - or rather just behind - the fret, there is no buzzing. I don't know how to upload pics here, so I'm going to make a little illustration by using signs.

| = Fret
F = Finger

|.....F.....| - Fret buzz.

|..........F| - No fret buzz

I'm pretty sure that the buzzing is coming from the fret that the string is meant to be touching, and thus not the subsequent fret, which would've meant low action. Because if it was the subsequent fret, it wouldn't help if I moved my finger from the middle of the two frets to just before the fret that I want the string to touch. I don't know if it makes sense to you. The fact that the placement of my finger stops the buzzing also tells me that it's not due to some loose parts inside the guitar, and neither does it sound like. It has got something to do with the frets themselves. And they aren't worn. They look and feel just fine.

I've been playing for 15 years, so it's not because of bad technique. I know how to play guitar. Furthermore, a guitar should be able to produce a non-buzzing sound when pressing in the middle of two frets, else barre chords would be impossible, since the ring finger can't be placed elsewhere when doing that.

My guitar is completely unplayable, and I really don't know what to do about it. I could take it to a luthier, but I'd like to hear your take on it before I spend a fortune on something I might be able to fix myself.

As I said, I've tried humidifying it. I've used a kitchen cloth, which I soaked and rang out and placed in a cut-open plastic bag and then sealed the guitar totally and placed it in a case. I've added humidity 2-3 times during the month I've been humidifying my guitar, to make sure that it was always humid.

The top/deck of the guitar looks a bit sunken - just like it did before I started humidifying it, as if the humidification hasn't changed anything, but I'm thinking that a month of humidification ought to be enough? Or am I wrong?

Best regards.