Find and Fix Rattles and Hums on Acoustic Guitars

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Excerpt from the May/June 2022 issue of Acoustic guitar | By Martin Keith

Does your acoustic guitar have a hum or rattle that you can’t find, let alone fix? You’re not alone. Here are some tips for finding and fixing those annoying clicks and buzzes on your acoustic guitar.

I’m having issues with string rattle on my 2018 Gibson Hummingbird Rosewood, especially on the high end. I’ve tried many brands of strings, but that didn’t fix the problem. What could be the source of the knocking? David Henry

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I’ve driven the rattles and buzzes out of almost every part of an acoustic guitar. Some are easy to diagnose and fix, while others can drive a person crazy. A beautiful guitar like yours will vibrate from anywhere, which means a rattle can come from anywhere. Therefore, I generally take an end-to-end approach when looking for a rattle or buzz. Here are some suggestions:

The most likely cause of the hum 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 angled back slightly, it can cause buzzing on 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 string vibration 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 that way, those string areas can vibrate against the frets. It’s easy to check – just put a calling card under the strings around the second fret and see if that fixes the problem when you play higher.

If the frets aren’t to blame, there are a few other places to look. In acoustics, my next stop is usually to check the bracing, as loose bracing can easily cause mysterious buzzing and rattles. I use an inspection light and 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 emit a clear sound. If there are any loose braces, you’ll likely hear a paper rattle mixed in with the sound. Strategic tapping of various areas can sometimes identify which brace is at fault. This should be done separately for the top and back; the back braces could just as easily come off.

Next on the list: two of my favorites. Modern tuners are held in place by a hex head ring with a washer underneath, which sits around the string post at each tuner. These come off very often, probably due to shrinkage of the wood in the headstock itself. If the washers are just a little loose, they will vibrate and make noise. Check this by tapping on the headset to see if you hear any metallic clicks or buzzes. If so, tighten the hex nuts at each tuner – almost all modern tuners use the same 10mm hex size. This can be done without removing the strings using an open end wrench.

Release the strings, pull each bridge pin halfway out of the bridge and tug on the string to make sure it is firmly seated against the bridge plate inside the guitar.

If that doesn’t fix the problem, it’s time to check the other end of the rope anchor: the ball end. Most acoustic guitars have pin-style bridges. I frequently find that the strings, especially the larger diameter bass strings, are settled into 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 windings, anchors the string in place with the end of the ball still hanging down a bit in the guitar. When I first encountered this I had spent almost an hour trying to locate the source of a mysterious and maddening vibration that just wouldn’t go away. After correctly reinstalling the ball, it was gone. Release the strings, pull each bridge pin halfway out of the bridge and tug on the string to make sure it is firmly seated against the bridge plate inside the guitar.

If the guitar is equipped with a pickup/preamp system, make sure the screws, nuts, and mounting hardware are tight and check that the cables and wires inside the guitar are securely anchored. The small self-adhesive cable ties inside guitars often come loose – after sanding there is often a lot of very fine, powdery dust in 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 the inside and then clean the clip location with rubbing alcohol, just to make sure it will stay in place.

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A final 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 is tight. (This is also a good time to make sure the neck is properly adjusted!) If not, you can gently add tension to see if the vibrations go away. Of course, this can change the guitar setup. If tightening the stem causes too much back arcing for good playability, it may be worth going to a luthier for repair. The approach I’ve used successfully in these cases is to remove a fret somewhere in the middle of the fretboard and drill a small hole through the fret slot and into the truss rod channel. Then, using a syringe, I force yellow wood glue into the slot. It won’t stick to the metal rod, but it will fill any space around it and prevent annoying vibrations. Sometimes sub-fret processing is required – it depends on the manufacturing tolerances of that particular truss rod slot. Then reinstall the frets and hopefully the problem will be gone.

The above list is just a brief overview of the likely causes of acoustic guitar buzzing and clicking. There are more, and I’ll probably keep learning new ones as long as I keep working. I hope this little checklist will help you isolate the hum in your Gibson, so you can get back to playing!

You have a question?
Not sure about the care and maintenance of your guitar? The ins and outs of guitar making? Or another topic related to your equipment? Ask Acoustic guitarMartin Keith’s repair expert by sending an email titled “Repair Expert” to [email protected] and we will forward it to Keith. If your question is selected for publication, you will receive a free copy of AGit is Acoustic Guitar User Manual.

This article originally appeared in the May/June 2022 issue of Acoustic guitar magazine.

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