I glued one to a tin can once and kinda mate a plate reverb
Not sure how you could really attach it to the string really though
If you could I bet it would make a interesting noise
I think maybe the spring is connected to some kind of electromagnetic pickup on the ones you get in guitar amps
I read somewhere that you can drill holes though and even chop bits off a piezo and they will still function, so why not drill through one and attach it to one end of your spring? Piezos are orig used for output, buzzers and stuff, so why not amplify one at the other end of your spring to see if you can create a timed loop as the noise travels along the spring and feeds back to the first piezo?
that's the basics of a reverb tank, low power amp & driver on one end of a spring, pup at the other end.