Thumping noise when hammers return and hit felt rail

[hearnm]

Hi there,

I have a Schimmel C126T upright piano, which I have a question about.

When I press and release many of the keys on the right hand side of the keyboard, there is a "thumping" sound when the hammers return and hit the felt rail. This sound isn't present on the keys on the left of the keyboard.

Now that I've started to hear it it's really beginning to get distracting, but I'm not sure if this is normal or if there is some adjustment that could be made to get rid of the sound?

The piano was bought new in 2022, and the only major thing that my tuner has done since then is to reduce the depth of touch to 10.5mm (which is apparently schimmel's recommended setting) to cure a problem that had initially been caused by humidity and witch had (prior to this adjustment) resulted in the keys producing a "stringy" sound.  He did this by inserting felt washers underneath each of the keys.

Has anyone come across this issue before, and is it just one of those things or is there something that can be done about it?

I'll see if I can attach a recording for reference.

Many thanks,

Michael

[hearnm]

... here is a recording as promised.

Many thanks,

Michael