When damper wire is not riding against guide rail bushing (not touching one side of the bushing), the damper head is likely to shake or move irregularly going up and down. This can be adjusted in the piano by bending damper wire. The bottom bend is for spacing, the top bend is for squaring. The top and bottom parts of the wire shall be parallel. The video is what I learned so far these years. As time goes by in the future, hopefully personal damper skill could improve.