There is nothing more annoying than a mysterious sound coming from your cello while playing. The cello body (being a big, resonant box) tends to amplify not only your beautiful music, but unwanted sounds, too. While seated with your cello almost every buzz sounds like it is right in your ear, so identifying where the buzz is coming from can be very challenging, even for an experienced luthier, and is most often a process of elimination.
Here, in descending order, are the most common causes of a cello buzz that we have found in our shop.
Knurled Nut at Tip of Endpin is Loose - Endpins that have a threaded, brass keeper (like the one shown here) are the most frequent cause of a buzz. As you play the cello, it creates vibrations, which can loosen that nut over time, causing it to vibrate along with your cello. You will hear it as a buzz. See this video by Linda West on how to fix that problem.
Seam Opening - Your cello's top plate and back plate are glued to the ribs (the sides of your cello). This glue joint is referred to as a seam. Seams are glued using hide glue, which is a light-weight, natural glue commonly used in bowed stringed instruments. It's main duty (besides holding your cello together) is to let loose if the top or back swells or shrinks too much, helping avoid a crack in either plate. It's common for your cello seams to open, especially when the weather dries out. The space that opens up may only be an inch wide, or it could be the entire length of one side or all of the top bout or bottom bout. These small openings along a seam can result in a buzz. Sometimes the seam can be open, but only on the inside, which will create a buzz. See this video by Linda West on how to find open seams in your cello.
Buttons or Jewelry - things you are wearing can buzz against the back of the cello. The most likely culprits are buttons on your shirt. Jewelry, especially necklaces can also buzz, and really should not be worn while playing as they can also damage your varnish. Purchasing a cello bib can help with this problem, then you can wear whatever you want!
F-hole Varnish Connection - If the varnish was applied on your cello in a hurried manner, drips can connect the narrowest area of your f-hole. Over time, these drips will break away from each other and can cause a buzz as the 2 pieces rub against each other as you play. If you work carefully with a small piece of folded sandpaper inserted into the f-hole, you can gently sand away the extra varnish that is touching.
Fine Tuner Adjuster Loose - Your fine tuner screw pushes down on an arm which pulls on the string to tighten it. Both the string adjuster or screw can vibrate if the little thumb screw that tightens your fine tuner does not have tension on it. Reach down and screw each fine tuner in a bit, making sure to get contact with the adjuster, which will feel like resistance as you tighten the screw. Loose screws are one of the first things we check in our shop when someone complains about a funny noise or buzz.
Add-on Old-style Fine Tuners - if you have a wooden tailpiece with one or more old-style, metal fine tuners installed, these are often a source of unwanted buzzing. These chunky, heavy tailpieces are often the first thing I'll suggest replacing during a setup consultation. Lightening the weight of accessories on your cello is a guaranteed way to open it up and make it more resonant. The best remedy is to upgrade your tailpiece to something more modern, and light-weight. The Bois d'Harmonie tail pieces in boxwood, ebony, rosewood and pernambuco have very light-weight composite tuner mechanisms. The tuners operate very nicely, and the lightness of the entire tailpiece will allow your cello to resonate more freely. The budget version of this would be the Wittner 'Ultra' Cello tailpiece. Fully composite, it is both light-weight and inexpensive.
Tail cord adjustors - While we are on the topic of tailpiece, we might as well mention one other culprit - the little threaded tubes (sometimes metal, sometimes plastic) that are used on some plastic tail cords to adjust the length of the tailpiece cord. Unfortunately, to inspect these threaded tubes you will have to take the setup down and pull the tailpiece off. But if you feel adventuresome, after eliminating the more likely options, you might want to check this out. You may be able to reach under your tailpiece and see if you even have this sort of tail cord nut before you start taking your strings off, though.
A Bad String - A string gone bad is by far one of the more difficult (and expensive) buzzing sounds to track down, but it is possible for a string to go bad, even a brand new one. You will hear it as a very high pitched, tinny sound. We have had brand new (expensive!) strings in the shop 'buzz'. And we can only assume that the winding has come loose from the core. The only way to see if this is causing your strange sound is to start changing out strings. Since all of your strings vibrate when you play, this is super hard to diagnose. If you are close to a luthier, they may be able to help because they always have used strings that can be swapped out one at a time to see if that solves your buzz.
That Little Plastic String Tube - you know, the one that is supposed to go on top of the bridge to keep the string from digging into the bridge? Yeah, that one. If it is just hanging around between the bridge and your tailpiece it's very possible that is the source of your buzz. We don't always see these tubes on cello strings; it's more common on violins. We usually just rip them off and throw them away and use bridge parchments instead.
Endpin fitting and/or Endpin - other parts of your endpin fitting or endpin can come loose and buzz or rattle. Cotter pins, tightening screw, collars, or the fitting itself not being properly seated in the endpin block hole can all cause a variety of sounds, including knocks, rattles, and buzzes. Get a friend to help you by holding various parts of the endpin and fitting one at a time while you play to see if that eliminates the noise you are hearing.
Fingerboard Issues - if your fingerboard is starting to come unglued from the neck, this can cause a really annoying buzz as it flaps against the maple neck. Also, if your fingerboard has warped or worn over time, strings can buzz on the high spots, especially if you have really low action. (If this is your problem, you need to have your fingerboard resurfaced)
If it has become drier where you live, and all of a sudden you have a string buzz, be aware that as your cello's top dries, the arching will decrease, which will take the bridge with it, in essence 'lowering' your bridge, which will lower your action. For players who travel a lot, or live in an area with extreme humidity changes throughout the year, having 2 bridges is a good idea. Both should be cut and fit for your cello; one left high for the dry time of year, and one lower for the humid time.
Another issue that we have seen that causes buzzes are tapes on the fingerboard to mark the finger positions for beginners. If the action is really low, the strings can end up buzzing on the tapes.
Nut Grooves - the nut is the piece of ebony at the upper end of your fingerboard that your strings go over as they feed into the pegbox and onto the pegs. If the nut grooves are not properly cut (as we will often find on 'budget' cellos) this can cause a buzz as the string vibrates against the front of the groove. It usually sounds more like you are playing a Sitar instead of a cello, with a twangy, tinny sound. You can sometimes find this problem by pushing down on each string below the nut one at a time as you play. If the buzz stops, that's your problem. Your luthier will have to help you correct the grooves.
Ornamental Pegs - pegs with ornamental collars or balls can often vibrate as the glue joint between the peg and the ornament fails. Check each one of these little ornaments to see if they are loose. A small drop of super glue carefully applied right next to the joint between the ornament and the peg will wick right into the joint and stop the movement.
Your Bow! - believe it or not, I have found buzzes in the bow itself. I once found bits of metal rattling around inside the tip of a carbon bow. Your bow has mortices (square-sided holes) in both the tip and the frog end. The hair at either end is held in place with hand-cut, small wooden plugs. If some random material gets in there, or something breaks off, it can cause a buzz or rattle. Also, the tightening button can come loose and rattle, as can other parts, such as the winding.
Splinters on Interior Blocks - some of the more mysterious buzzes originate from inside the cello, and are only found by sticking a camera on a flexible shaft through either the f-hole or endpin hole, and illuminating the inside of your cello with a good light. Occasionally, we have found splinters on either the neck, endpin or corner blocks (much more common on corner blocks), that will vibrate, usually with weather changes. It's almost like having a reed instrument, like an oboe inside your cello! More likely on older, or cheaper instruments, this is a really tough buzz to find!
Dead Bug Carcasses - yep, you heard me right. Typically found only in older instruments with obvious worm damage, if some sort of insect burrows into the wood of your cello, then dies, it's dried up carcass can often cause a very annoying little buzz as it's skeletal remains vibrate against whatever worm hole they are hiding in. This is extremely rare, and only found in really old instruments. So, if your cello is older, and has signs of worm damage, I wouldn't rule this out if you have eliminated every other possible source.
Older Repairs and other Random Issues - older repairs, typically inside your cello, can be the cause of buzzes. Things like a bass bar coming loose, cleats coming unglued, or little splinters on the sound post can all be possible sources of strange noises. Purfling in older instruments can come unglued and buzz.