Harmonic, sympathetic, overtone, ringing, ect sounds. Some find this annoying. It’s the sound of the strings between the bridge and tailpiece. The sounds can be created while playing as the bridge vibrates. You can hear it by strumming between the bridge and tailpiece.
There are several ways to mute this. Leather woven between the strings, Velcro or fabric, rubber grommets, even tape. Also leather and such in the tailpiece. There are several more decorative methods using a suppressor.
Most suppressors are wooden with grommets on each end and fabric/leather and such in between the grommets. The grommets on the ends fit between the outside strings and the material in between mute the remaining strings. The first I saw of these was the Weber Wood Nymph by Vern Brekke. These can be made for other arch top instruments as well.
Our suppressors are made in this manner. Many of which are inlaid making them functional jewelry.
