dampers

I'll try to give my opinion. One must look at the pedal regulation. But tuning (and the state of the hammer rail) and temperament also have a great influence.

I am actually quite experienced with this problem, having had it in the past on my piano.

It probably depends on the fact that they do not rest well on the string trichords even if to the eye it would seem so; they might be not entirely, how should I say, "resting" because they are deformed in their length, leaving that slight halo. It is not certain then that it depends on the note in question, but it could depend on another string from another trichord that enters into resonance by sympathy with the trichord in question. One should try to understand which ones, however if one needs to be changed, it is better to change all the damper felts, at least all those of the same type/section, otherwise one would notice the difference between old and new.

Camillapiano, they answered you well! It can depend both on the wear of the felts and on their centering (especially in the bass). First try to regulate and center them. As for regulation, I recommend adjusting the escapement point (almost halfway through the hammer stroke) and adjusting both the transverse and longitudinal orientation. It's a job that requires patience! I know you have already done it... but if after a further check the problem persists, I would replace the felts (felts woven with a longitudinal weave..... they cost more, but they are better.... it takes a good technician...)

thanks for the answers.

can I easily find longitudinal weave felts?

I usually buy from FTP

Yes