I bought a Warwick Corvette off of E-bay. I put some new strings on it when it arrived and did a minor setup on it. I got the action the way I liked it, but there was buzzing on the G string when it was fretted. It is most noticable on between frets 2-7, but it buzzes all along the fretboard. I then raised the nut height, and the string height at the bridge, but the buzzing is still there. And it is only on the G string. I like my action on the low side, and I have a medium attack. The other strings buzz when I dig in real hard, but not when I pick normally. The neck looks to have adequate relief, after I loosened it a quarter turn.

Does anyone have any ideas?

You can probably lower your nut back to where it was. It is only a problem if the string buzzes when it's played open. Actually, this may be contributing to the problem because you have higher apparent action as a result of a high nut.
If you look down the neck at the edge of the frets from the headstock end you might be able to see a problem. Probably a renegade high fret.
Another thing you can do is set the neck straight and use a short ruler to check for high frets. Just move it up and down the neck trying to rock it on the frets. Any high frets will become apparent pretty quick.
Of course, any competent repair person should be able to fix this without too much trouble.
Good Luck

If the buzz is coming from between the nut and the fret, it's usually a nut problem, otherwise it could be that the frets need dressing