3g?

I'm not familiar with your guitar, but one possibility is Stratitis (web search this term for an in-depth explanation). Try lowering your pups, especially any neck or middle position pups --or maybe just the G polepieces on these, if adjustable. When the magnetic pull is too strong and focused on a string, it can create an unwanted node that produces strange vibrational modes. This is a malady first noted on Strats -- hence the name. But again, this is just a possibilty.

Jackson Warrior, right? If gnease's suggestion doesn't apply, maybe one of the fine tuners is loose or too far one way or the other. When you change string on an instrument with fine tuners I think you have to 'center' them before tuning with the headstock tuning pegs (before you lock them down) so you have an equal amount of sharp/flat movement. With the older strings you might've been fine tuning to the point where the screw is rattling around in the saddle piece.

Do you hear the sound when you're not fretting - i.e. playing it open?

No i do not hear that sound when i play it open. I only hear it when i fret it. Im gonna try Demos advice. Any more?

if the gauge of string or even the manufacturer of the string has changed the tension is different,so the trem wont float like the factory setting,i have a dean phantom ml,i changed from ghs boomers to the dimebag signature strings an the trem was right angle from the body!

my advice is to choose your fav string gauge for the relevance of sound and comfort,take down your local luthier,an say"set this up so i can use _____strings"it costs about £30[if youre english!]

all the best

dimebag

Lay your finger on the string block at the trem then pick the note and see if it goes away. Mine did the same thing and it ended up being the block had fallen out of the screws guide and was not sitting straight.

Well demoetc was right. THANKS. Yea, i just tightend the tremelo tuners half way down and retuned it worked perfect thanks. :D

cool man :)