Sometimes dampers wobble as the key is pressed, especially on a hard blow, and can actually produce an audible vibration (a strange and annoying sound). Dampers with extended wires (usually at tenor/bass breaks) are particularly prone to this.
There are 2 remedies:
1 Replacing the wire guide felt.
2 Cutting back the damper head and re-cranking the damper wire (so that the damper head protrudes less, and so vibrates less).
Usually, both remedies are required – though as you can see from the pictures, only a 1.5mm thick sliver had to be removed, and the head sits just that amount closer to the plate arm…and now doesn’t vibrate!