Unwanted string resonance-What can do about this?

[gimmeagig]

I have a strange problem on my Atelier Z 5 sting.When I play a note on the A string 4th fret C#, the section between my fretting finger and the nut rings in a high pitch and it's audible and I can't mute it because it occurs below my fretting finger. The other strings do it as well but not to the same extent.
So in other words my strings vibrate freely from my fretting finger backwards to the nut.
I have relief in the neck but not a whole lot.enough for a business card below the 7th fret maybe. Action is pretty low but not ridiculous and the bridge is set to follow the radius of the neck.
But that I guess doesn't matter because the problem happens below my fretting finger.
So when I press down on the fret, that action alone triggers the higher unwanted pitch.
I was thinking It could be that the nut is not slotted deep enough but it looks fine to me.Probably 2 credit cards thick from the wood to the bottom of the string.First fret to bottom of the string is about one credit card. I'm not sure if strings should lie flat and touch the frets from the fretting finger back to the nut or if the clearance i have is normal.
What do you guys think, Any ideas?

[testing1two]

Your instincts are probably correct about the nut slot being too deep on the A string. To test this, hold down the 3rd fret and measure the gap between the string and the 1st fret. You should be able to slide a piece of paper in the gap, which means the clearance is .003-.005". If the string is touching the first fret than the slot is too deep.

[walterw]

ah, the mysterious, unpredictable "back-buzz".

you might indeed have to raise the nut a pinch, and/or relax the truss rod a bit.

[gimmeagig]

Actually it's not back buzz it's a ringing of the string from my fretting finger back to the nut., so I was more thinking I might have to lower the nut. Am' I right about that?

[Turnaround]

Originally Posted by gimmeagig

Actually it's not back buzz it's a ringing of the string from my fretting finger back to the nut., so I was more thinking I might have to lower the nut. Am' I right about that?

No. There should be a bit of clearance between the string and the frets on the nut side of the fretted note. If you lower the nut enough that the string won't resonate between the nut and the fretted note, it will buzz on the first fret when the string is played open.

[walterw]

that's what back-buzz is, the length of string between the nut and your fretting hand making noise.

[trevcda]

Is it coming through the pickups/amp or is it just something you hear when playing unplugged? If it's the later, I wouldn't worry about it.