Feedback?! Harmonics?!

Why is it.. some notes turn into feedback faster? Is that what natural harmonics are?
What I mean is.. when Im soloing over song thing.. there mite be a note that when I pick it.. it quickly turns into a feedbacky tone really quickly. Where as a fret up or down from it will ring out for longer before fading.
Why is that? Are all guitars different? Or is it always the same notes that do that? ANd whats it called!!

I use Gibsons and a big marshall stack if thats why I get feedback so easily!

I think it is dependent on A) the frequency of the note and its harmonics, B) the resonance of the guitar (wood) and the C) the acoustics of the room you are in.

yeah, feedback is tough to predict and get a handle on.
It's so dependent on so many factors that you can't plan too much ahead for it.
I remember years ago in one of my first bands, there were some tunes I used to use controlled feedback on. I had it down to an art in our practice room.. knew exactly which way to point the guitar and what notes to hit.
Then the first time we played live I couldn't get any feedback at all.
I looked like a total idiot waving the guitar in front of my amp and just getting this screaching noise.
After awhile ya learn not to rely on it but to just use your intuition and improvise. If it happens.. great. If not, just shrug your shoulders and wait till next time.

Oh well.. I take it a feedback enhancer would make all notes sound like that.
Its not like feedback though.. not the traditional feedabck I mean.. like screechy or sounding like god zilla! Its this sweet tone! its amazing!!

Or try playing a semi-acoustic hollow-body !!

Wotcha mean?