Buzzing string?

[AudioDwebe]

I picked up a used Renaissance fretless on Monday and when I got it home to play, I heard a buzzing sound coming from the bass whenever I played the G string. I heard it on one amp, then another, and finally through a headphone rig.

Buzzing. I was afraid the preamp was toast.

I unplugged it and started to systematically tighten all screws. Not many screws and none of them were really loose.

Then I played the string again acoustically. I still heard a buzzing. I plucked and listened all over the instrument trying to locate where the buzzing was coming from.

Then when I listened by the fretboard, the buzzing sound was louder. My ear when up and down the board and sure enough, the buzzing was coming from it.

I then looked to see if the string was somehow touching the board - it wasn't. Then I removed the string and tapped along the board to see if any part rattled - it didn't.

Then, on a whim, I decided to take the G string from my Carvin fretless and place it onto the Turner. No buzzing.

I then placed the string from the Turner onto the Carvin - buzzing. The string was buzzing. Couldn't believe it.

I then returned the original string back onto the Turner, realizing that I'd have to get some new strings really soon. However, when restrung with the same damn string, the buzzing was gone.

And it's still gone.

What gives?

I was told by the seller that the strings were Acousticore, but they're black and when I looked at the TI Acousticores online, they all looked white. So the strings my not be what the seller told me they were (among many other things...worst buying experience ever!).