If it's on the soundboard the best way is with the right length of cam clamp but if that's not possible or if it's a back brace you'll need an expandable prop which you can make from those coupling tensioners which have a centre piece with a left hand thread on one side and a right hand on the other. Now if you find a loose brace with the spatula you will need to work out how you are going to clamp it. Of course before doing this, check the screws in the machine heads and check that the strings are neatly tied with no ends rattling behind the bridge. Sometimes it helps to get a mirror and a good light in there too but usually the feel test with the spatula will find it. Often this will be the only way to find such a buzz. I have a metal art spatula which I carefully place against the edges of the braces, which will slip under if they are loose anywhere. I recommend tapping the back with a knuckle and carefully tapping the soundboard but if nothing is obvious you'll need to get your hand inside and have a feel of every brace. A loose brace anywhere can cause this and the back braces are often loose. There is no reason to say it's unlikely to be a back buzz.

If the buzz only occurs at a particular pitch it's more likely a loose brace, but if you change the tuning and it still occurs on the same fret, it will be the fret.

Try tuning the G down a semitone and play the first fret. Is it a very obvious buzz? Unlikely to be a back buzz.

wrote:Try locating them on a steel string, it's even worse!

Buzzing past 12th fret