- https://youtu.be/0YtK9367R4Q?si=msLUTWWy3QbToR1H
Start by checking if there is any displacement of 'the damper wire' towards the sounding string. If the (H) string does start buzz when the hammer hits it lightly, this could potentially be the cause. Move the damper wire slightly to the side from the string to observe and hear any buzzing there. If you're comfortable, try pressing on the wire to see if the rattling goes away.
To further investigate the issue, examine how each of the three strings sound separately in the (H) string choir using a plectrum. Pluck each string individually while listening for the problematic buzzing string. Additionally, pay attention to the positioning of these strings on the wood bridge. Determine exactly where the buzzing is coming from.
It is likely that the buzzing issue is related to the following reasons:
1 The bridge pin of one of the strings may have moved or become loose. There could also be debris, such as metal shavings, between the string and the pin of the bridge.
2 Oxidation might have formed between the pin and the string.
If you feel comfortable, you can try the following steps:
1 Wipe the problem area with denatured alcohol.
2 In rare cases, for double strings (H and B), inspect 'the pinch' on the iron plate. There could be foreign objects or dried paint from the iron frame in that area.
3 Check if the wood notch for the bridge pin is correctly cut for the individual strings.
4 Lastly, tighten all the screws that hold any metal components on the piano using a screwdriver.
Good luck!