Nice try, Youko-san, but unfortunately that is not the right answer :-)
Korean sometimes adopts foreign words as is, but 건(gun) is not one of them.
건들건들 is one of those expressions directly imitating a sound or action (onomatopoeia). It is an adverb, and you must add -거리다, -하다, or -대다 to it to make it a verb.
It describes something gently shaking or swaying, like a branch of a tree, a loose piece of a structural member, a loose tooth, or any such things.
For example you can say 이빨이 건들건들한다 (My tooth is loose), 창틀이 건들건들거린다 (The window frame is shaky).
건들거린다 has another meaning too - a person swaggers or acts in a frivolously showy manner like a street bum would (건들거리며 걷다). This is used for people only, usually male.