From the May/June 2022 issue of Acoustic Guitar | By Martin Keith
Does your acoustic guitar have a buzz or rattle you just can’t seem to find, let alone fix? You’re not alone. Here are some tips for finding and fixing those annoying rattles and buzzes on your acoustic guitar.
I’m having problems with string rattle on my 2018 Gibson Hummingbird Rosewood, especially on the high end. I’ve tried numerous brands of strings, but this has not corrected the problem. What could the source of the rattling be? —David Henry
I’ve chased out rattles and buzzes from nearly every part of an acoustic guitar. Some are easy to diagnose and repair, while others can drive a person crazy. A nice guitar such as yours will vibrate all over, which means that a rattle could come from anywhere. Therefore, I usually take an end-to-end approach when seeking out a rattle or buzz. Here are a few suggestions:
The most likely cause of buzzing is the frets themselves. A high fret will cause a buzz on a specific note, which is usually easy to determine. If the neck is slightly back-bowed, this can result in buzzes across a series of adjacent frets, usually in the lower third of the neck (frets 1–7 or so). Another, much more insidious cause of fret buzz can be vibration in the strings between the nut and the fretted note (i.e., behind the fretted notes). If the nut is a bit high and the neck relief is just so, those areas of string can vibrate against the frets. This is easy to check—just put a business card under the strings around the second fret and see if this resolves the issue when playing higher up.
If the frets are not to blame, there are a few other places to look. In acoustics, my next stop is generally to check the bracing, as a loose brace can easily cause mystery buzzes and rattles. I use a light and an inspection mirror, or in some cases an endoscope camera. However, loose braces can often be diagnosed by simply holding the guitar by the neck and tapping firmly on the bridge or around the top. The guitar should let out a clear thump. If there are any loose braces, you’ll probably hear a papery rattle mixed in with the sound. Strategic tapping of various areas can sometimes identify which brace is at fault. This should be done for both the top and back separately; back braces could just as easily come loose.
Next on the list: two of my favorites. Modern tuning machines are held in place by a hex-head bushing with a washer underneath, which sits around the string post at each tuner. These very often come loose, probably due to wood shrinkage in the headstock itself. If the washers are just a bit loose, they will rattle around and make noise. Check this by tapping the headpiece to see if you hear any metallic clicks or buzzes. If so, tighten the hex nuts at each tuner—nearly every modern tuner uses the same 10mm hex size. This can be done without removing the strings using an open-end wrench.
Slack the strings, pull each bridge pin partway out of the bridge, and give the string a tug to make sure it’s firmly set against the bridge plate inside the guitar.
If that doesn’t resolve the issue, it’s time to check the other end of the string anchor: the ball end. Most acoustic guitars have pin-style bridges. I frequently find that strings, especially larger-diameter bass strings, are installed in the bridge but not firmly seated against the underside of the top. In these cases, the wedging action of the pin, combined with the friction of the string wraps, anchors the string in place with the ball end still hanging down into the guitar a little. The first time I encountered this, I had spent nearly an hour trying to locate the source of a mysterious and maddening vibration that simply wouldn’t go away. After I properly reseated the ball end, it was gone. Slack the strings, pull each bridge pin partway out of the bridge, and give the string a tug to make sure it’s firmly set against the bridge plate inside the guitar.
If the guitar has a pickup/preamp system, make sure the screws, nuts, and mounting hardware are tight, and check to make sure that the cables and wires inside the guitar are firmly anchored. The small, self-adhesive cable clips inside guitars often come loose—after sanding, there is often quite a bit of very fine, powdery dust packed into the pores of the unfinished interior. This can make peel-and-stick adhesives much less effective. When installing cable clips in new guitars, I vacuum inside and then spot-clean the clip location with rubbing alcohol, just to make sure it will stay put.
A last potential culprit is the truss rod. On some instruments, the neck is stiff enough that the truss rod doesn’t need to do much. In these cases, the rod is sometimes loose enough to vibrate in its channel. Check the adjuster to see if the rod has tension on it. (This is also a good time to make sure the neck is adjusted correctly!) If not, then you can gently add tension to see if the vibration goes away. Of course, this may change the setup of the guitar. If tightening the rod sufficiently causes too much back-bow for good playability, then it may be worth a trip to a luthier for a repair. The approach I’ve used successfully in these cases is to remove a fret somewhere around the middle of the neck, and drill a small hole through the fret slot and down into the truss rod channel. Then, using a syringe, I force some yellow wood glue into the slot. This won’t stick to the metal rod, but it will fill up any space around it and prevent troublesome vibrations. Sometimes treatment under multiple frets is called for—it depends on the manufacturing tolerances of that particular truss rod slot. Afterwards, reinstall the frets and hopefully the trouble will be gone.
The above list is just a brief survey of the likely causes for buzzes and rattles in an acoustic guitar. There are others, and I will most likely keep learning new ones as long as I keep working. I hope this little checklist helps you isolate the buzz on your Gibson, so you can get back to playing!
Uncertain about guitar care and maintenance? The ins-and-outs of guitar building? Or another topic related to your gear? Ask Acoustic Guitar’s repair expert Martin Keith by sending an email titled “Repair Expert” to Editors.AG@stringletter.com and we’ll forward it to Keith. If your question is selected for publication, you’ll receive a complimentary copy of AG’s Acoustic Guitar Owner’s Manual.
This article originally appeared in the May/June 2022 issue of Acoustic Guitar magazine.