Sometimes the support braces on the inside of an acoustic guitar come loose. Usually you'll notice it when you start to hear an unexplained vibration in the guitar's body. Press down firmly on the top of the guitar while you pluck the low "E" string. When you press a spot and the vibration stops, that's where you have a loose brace. Now take all the strings off the guitar and reach inside. Find the loose brace and try to wiggle it. It may just be a little loose, or it may actually come off in your hand. If it comes off, don't panic. You can still fix it.

You will need wood glue and popsicle sticks. If the brace is still attached to the guitar, it will also help if you can find some kind of syringe with a tip wide enough to dispense glue and narrow enough to it in the crack between the brace and the body.

1. If the brace is attached, reach inside and squirt as much glue as you can into and around the loose spot.
2. If the brace has come off, practice placing the brace in the correct position inside the guitar a few times before you put glue on it. Then put a liberal amount of glue on the brace and put it back in place.
3. Take one of the Popsicle sticks, reach inside the guitar, bend it, and place one end against the brace being glued and the other against the opposite surface of the guitar.
4. Repeat the process with as many more Popsicle sticks as will fit along the length of the brace.
5. Leave the glue to dry.
6. Remove the Popsicle sticks.