thumping dampers

[Jon Page]

Its probably the bass and tenor wedges impacting the strings.

Are the strips long?  If so, slice them in half or cut a small wedge 
shape from the center
of each length effectively making four 1/2" blocks from two 1" strips.

This will soften the expansive surface and allow the damper felt to 
seat more effectively.

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Regards,

Jon Page