This is a fairy common issue which occurs most often with Cellos but can also affect Violins and Violas – it is called a ‘Wolf note’. A wolf note is an unpleasant howling tone which is produced when the note played matches the natural resonating frequency of the instrument. These frequencies are often found somewhere between the notes e and g# but can pop up anywhere on a Cello.  It is reported that some of the best cellos in the world have wolf notes, and professional players often learn how to play around the note using a combination of bow strokes

There are however, several ways to suppress a wolf note, and one of the easiest ways is to use a basic wolf tone eliminator. These are fairly inexpensive little brass weights which are quite easy to install. The eliminator is placed behind the bridge on the G string, about one third of the way towards the tailpiece.  Starting at about this point, move the eliminator up or down until the ‘wolf’ is slain!