Putting a resistor across the binding post or a cap in series with the tweeter will both tame the piezo, but in different ways. I found that the cap will attenuate the piezo, while the resistor "mellows" it out.Values you may want to try are:
0.1uF for -6dB
0.3uF for -3dB
Try a 50, 22, or 12 ohm resistor across the binding post for a small, medium and large "mellow" effect.
Gar.