Metallic "ringing" or resonance after damped notes

[Crowder]

I'm noticing something unusual with my mandolin. After a damped note I hear a metallic ringing or resonance that seems to be coming from the body. It sounds similar to what you hear if you lightly drum on the strings behind the bridge, or tap on the bridge itself, except without the initial attack.

Funny thing is, I have a piece of leather woven through the strings right at the bridge. As an experiment, I put a piece of sponge back there between the strings and the body to make sure the strings behind the bridge were completely damped. The bridge itself is a one-piece cast job, no cover.

I removed the truss rod cover and made sure the adjustment nut was tight, so that eliminates that possibility.

Is there anything else that could cause this? The bridge itself, perhaps?

[sunburst]

Try damping the strings between the nut and the tuner posts and see if the sound goes away.

[pops1]

Do you have a pickup in side? While it shouldn't make a ringing, sometimes the wire will vibrate against the top. Usually it's a buzz, but.....

[John Flynn]

I have a Rigel A+ Deluxe that used to do that when it was new and damping the tail and head strings did not help at all. What was happening, I believe, was that hitting the damped note sent some energy through the bridge that sounded a harmonic on an adjacent string. I could tell that because if I damped the adjacent string, it would stop. I wish I could tell you I found a cure other than time. After the first year or so I had the instrument, the effect diminished and finally went away.

[Willie Poole]

I have found that a string not riding it the nut slot correctly will cause a ringing vibration on the E string and maybe on others also, if the noise is present even when you strike a fretted string then that won`t be the problem unless it is not riding correctly in the bridge slot...If I was working on the mandolin I would make sure the bridge is fitted perfectly flush on the top to start with...

[Crowder]

For the curious, I diagnosed this ringing as coming from the strings behind the NUT (thanks @sunburst). Strange that I never noticed this before. I've had this mandolin since 2007. Might be something about the strings I chose.