After 35 years of playing and tweaking guitars and, more recently, mandolins and ukes etc, I've come across lots of different annoying buzzes. Not only do they turn out to have the same causes again and again, but I see the same questions about buzz over and over on forums.
So, just though I'd post a little summary of the causes of buzz that I'm familiar with, things to look for and how to fix.
First thing is to track down where the buzz seems to come from. Sometimes harder than you might think!
Here's a numbered list of symptoms. Under that is a list of causes that tells you which symptoms point to which problem.
1) Does it seem to be the headstock end of the instrument that buzzes?
2) Does it seem to be the bridge end that buzzes?
3) Does the instrument buzz or rattle if you hold the strings muted and shake it?
4) Does it happen just with open strings
5) Does it happen just when strings are fretted or with a capo?
6) Does it happen with open strings AND when strings are fretted or with a capo?
7) Do only certain strings buzz?
8) Does the buzz happen around certain frets?
9) Does the buzz happen only when certain notes are fretted?
- Worn/damaged/old/faulty strings: Symtoms 1,2,4,5,6,7,8,9 from the list above.
A change of strings can't hurt. So if it seems possible that the strings may be the culprit, why not change 'em and eliminate that possible cause?
- Loose hardware: Symptoms: 1 or 3 from the list above.
Firstly check for rattling tuners, loose tuner screws, worn worm gears, loose and floppy string-ends, loose tuner shaft bushes/washers. Tighten screws and loose parts, replace worn parts, trim strings.
- Nut issues: Symptoms 1, 4, or 7 from the list above.
Check that nut slots angle back and down towards the tuners. Check that there is no loose plastic/tusq/bone in the nut slots. Check that slots are not too wide for the string gauges. Check that nut slots are not cut too deep causing unfretted strings to buzz against 1st fret.
If you don't have the knowledge/tools to adjust nut slots then seek advice from a music store, luthier or guitar tech. I recommend the use of purpose made nut files for adjustments.
- Loose truss rod (rare in ukes!): Symptoms 1,2,3,4 or 6 from the list above.
Check to see if instrument has a truss rod (may be a cover on the headstock or a nut/screw at the body end of the neck as viewed from inside the soundhole). Check with appropriate wrench to ensure that rod is not completely slack and insecure. Tighten CAREFULLY until some bite/resistance is felt. This should stop most rattling rods unless the rod is faulty or incorrectly fitted. In that event, seek pro help.
- Foreign matter inside uke body: Worth checking with any of the symptoms above!
Shake it about, look inside and clear the stuff out!
- Loose/unsecured wires on electric models: Worth checking with any of the symptoms above.
Secure wires with ties or tape. If you need to anchor them to the uke body then try to fix to the instrument sides/ribs rather than the soundboard or back if you have a choice.
- Bridge issues: Symtoms 2,3,4,5,6,7,8 or 9 believe it or not!
If bridge is slotted (uncommon) then check the same points as for nut issues, except if slots angle down they should do so towards the butt end of the instrument - down and away from the headstock. Check that bridge saddle is not too low, causing buzz/rattle against frets. If too low then either shim the saddle to the correct height or replace saddle.
- Loose braces / struts: Symptoms 2,3,6,7,8 or 9 in the list above.
For some of these hard-to-locate buzzes, if you're sure they aren't vibrating pickup wires etc, they just may be loose braces. This is something you see quite a lot on old acoustic guitars - for some reason older Gibson acoustic guitars seem especially prone to it. Unfortunately, uke soundholes are harder to get your hands into than the ones on guitars, so it's not so easy to feel around. I'd suggest using a small light, a dental type mirror and something with which to prod at the various struts. Just check out for any obvious loose components. Shaking the instrument, or tapping the top can sometimes show up a loose brace.
A loose brace is not a disaster - it is usually a pretty easy fix for someone with experience and the right glue and clamps etc - but unless it is a very cheap uke, a trip to the luthier or guitar shop is the wisest way to get it put right.
- Fret issues: Symptoms 1,3,4,5,6,7,8 or 9 in the list above.
NB: Unless you have experience of adjusting frets, and the right tools, it is best not to go at them with files etc. Seek pro assistance.
Even though neck and nut end buzzes that vanish when you fret notes at the 1st fret usually indicate nut issues, it is possible that they may also mean a high or crooked 1st fret. To check, take a steel straight edge and lay it across the frets lengthwise. You should be able to (gently, so as not to score gouges) be able to slide the steel back and forth along the neck without the end of it snagging or bumping over proud frets.
To check for high frets nearer the middle of the fretboard, see if the straight edge rocks at all as if a high fret were a fulcrum. The steel should lie flat and even on all frets.
Worn frets, especially in low positions can cause buzz on higher ones, so check for wear.
A point on the fretboard where the same note sounds when you finger a string on two adjacent frets usually (in my experience) means a low fret. This will need to be replaced or the whole fretboard levelled. Paradoxically, this same-note symptom can also (rarely in my experience) mean a high fret!
The brave may attempt to level frets by tapping with a light hammer to ensure they are seated properly, or levelling with a flat file or flat, unworn grinding/sharpening stone. After filing, frets will require rounding and polishing. Best done by the experienced.
I'm sure I've missed out loads, so I'll pop back and add as I remember stuff.