The piano I'm messing around with has an issue in the midrange where certain dampers don't sufficiently damp the strings when they return after a note is played, leaving single notes playing on for a rather irritating result.
Is there a way of solving this? It's a grand so I thought the dampers are returned by gravity...

Also, in the midrange, the leftmost strings of several notes buzz very faintly but do not ring out. Are the hammers displaced too far to the right? What else could be causing a buzz that dies after literally 1-2 seconds, instead of the clear note of the other two strings in the note?

It is usually not to difficult to diagnose problems with grand dampers, but fixing them is often an all or nothing proposition: You may need to go back and redo all of them to fix a problem with a few of them.

Possible problems are wear, including wear on the key end felts, keys which are not leveled properly, including worn back rail cloth, broken springs on the underlevers, etc.

I have posted the procedure for setting grand dampers a couple of times. You might do a search to find it.

I've occasionally noticed this on one note on my Steinway B. It seems more related to periods of high humidity than anything else. When things dry out the damper returns normally every time.

That is probably a tight center pin joint in the underlever.

Interesting, BDB. I had wondered if it originated deeper inside because the damper itself seems just as free as the others in it's bushing. I'll have my tech look at it when he comes for my fall tuning.

If it's not the centre-pin bushing, it could be the bushing in the damper guide rail.

You could try reaming out or ironing the bushing, and cleaning/polishing the damper wire

with fine-grade wire wool.

(you obviously need to remove the damper to do this).
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it could also be that a few damper set screws have loosened up and are not tight enough allowing the damper wire to turn ever so slightly in the damper lever. If this happens, the damper felt will just barely catch between the strings especially on bi-chords. Let it go long enough and the dampers can form a funny crooked angle always wanting to set in that new resting position outside of strings ringing through. In the tenor near the bass area, this is often the touchiest of places to seat dampers. The dampers are often smaller near the harp there so there is not much room to move them or always get at them easy.

If that's needed my tech will be the one, not me.

FWIW, the damper in question for me is the F above middle C. It sticks in the full up position occasionally (as I said, really only when the humidity has been high) when the note is played w/o the damper pedal.

My guess would be the damper guide rail bushing Howie.

Thanks, Jerry! This stuff fascinates me. Even when it's not quite functioning properly. Maybe I ought be a tech rather than a dilettante pianist!

Sometimes the damper wire is leaned to the side with too much pressure. A slight bend to the wire may work. You can hear the wire rub against the bushing when pressing the damper up with the underlever when too much lean is present.

When a damper stays in the up position it maybe locked up by the sostenuto rod. I've found this problem in some Steinways and other fine grands.

I've solved it by leaning the damper wire away from the sostenuto rod and/or by properly aligning the rod.

I don't think my problem is quite as bad as that of BDB, as the damper is resting on the strings, just resting with insufficient pressure to have a complete effect... I would have gone for the spring but wouldn't that affect all dampers? And the few dampers move as freely as the normal ones, they just don't rest with as much pressure on the strings.

Remove the action and watch the damper very carefully as you raise and lower it with the damper lever. Is it coming up and down perfectly straight? Leaning to the left? Right? Leaning frontwards or backwards? Is there a slight twist in the damper head so it is not seating squarely on the strings? Is there ANY, even a little teeny weany bit of friction upon lifting or lowering of the damper slowly or quickly? Lots of possibilities... Worn damper felt? Crooked felt? Crappy felt?

Im removing the action to reface the keys this week so I'll check!