I posted a link about resonant frequencies, and dead/thuddy notes last week. Most stringed instruments have them somewhere, and my only gripe is when they fall on an open string. The note you're hearing is actually louder than most others, but cancels itself out. Combined with the lack of sustain, it appears dead. I just had two Martin concert ukes with a thuddy G note and open G string, and both were returned. I made a video, but can't get the vimeo link on here. In any case, here is what luthier Aaron Green wrote regarding this issue:
"Any time you have a booming note on the guitar, there is a resonance that is very active around that frequency, not just the main cavity (A0) resonance. Very often what is known as the cross dipole on the top comes in around A.
In any case you have to understand the underlying issue here. Guitars vibrate in many ways all at once. There are innumerable resonances that interplay between the top, back and air inside the guitar. How they all relate to each other is what determines the charecter of the guitar. What makes building such a challenge is that most desireable qualites have a contridictory relationship with each other. Evenenss of response is desirable, so is an expansive tonal pallete and a sound that is intersting to listen to. These two qualites are odds with each other. What creates an even sound is a flat frequency response, all the resonances behaving at the same level. Speak in a monotone voice and you'll get the picture. What creates an interesting sound is a lot of active resonances, what my teacher called "peaky" when we would look at a frequency plot chart (kind of like an EKG moniter).
The real trick is to strike the balance between the two, which is lots of active resonances that behave in a controlled fashion. I tend to think of this desired interplay of the resonances like a bunch of gears. Each resonance is represented by a spoke in a gear. If they all fit together well, when one resonance peaks another one will come and fill the dip it creates. The result is an even response that still has lots of charecter and tonal capabilities. Hard to do to say the least but you only hit as high as you aim.
Some designs lend themselves to one side of this more than the other, lattice and double top guitars can to be very even, but lack the pallete of a "traditional" guitar. And very often you'll see a "traditional" guitar that is quite musical and colorful with some real booming notes, particularly guitars that are underbuilt.
Some uneveness of response, in a new guitar can be expected to take care of itself, if you take the time to really work the notes around the boomer. I have heard it in my own guitars, but it wasn't a glaring problem nor were there dead notes surronding the boomer. I would still have to say though that if you don't like the guitar from the get go, it is unlikely you will like it later."
Aaron apprenticed with Al Carruth, and has become quite an accomplished luthier over the past decade or so.
Even after explaining it to them, they always say, "The notes all sound good to me." The Martin in that video had a fretted G note on the C string that sounded like a hammer hitting a board, and sustained for a millisecond.
