"hollow" sound

gypsystuff

Hello,
I own a GJ guitar from a pretty decent luthier (i prefer not to mention his name).
overall, it's a very good instrument. but it always had the problem of some "hollow" sound from some places over the neck. for example, the 10th fret on the D string and the 17th fret on the G string.

What do i mean by "hollow"? i don't really know how to describe it. it's like this preticular places don't have any sustaine (no resonance).

what could be the problem?

second, latley i've noticed some rust on the tailpiece and even frets.
i take really (and i mean, r-e-a-l-l-y) good care of the guitar. the temperatures are pretty stady, no high humidity.

what could be the problem with the rust? can i clean rust from the tailpiece and frets or should i buy a new one (tailpiece) and replace the frets?

thank you very much

Jazzaferri

If it's from a pretty good luthier I'd call him and discuss the problems with him. See what he says and what might be done about them.