When the key (F#3) on a grand piano is pressed a sound produced clearly a chord instead of a unison.

[maxim_tuner]

• In this video, we can observe that when the key (F#3) on the grand piano is pressed, the sound produced clearly resembles a chord, rather than the intended unison according to the technical specifications. What is the cause and why does this happen there?
  
  By the way, when the key is pressed more forcefully, with increased intensity, we can clearly hear a triad there. The reason is simple - two strings of this three-string sector, where the hammer strikes (F#3), have non-standard tension and have become slack. In other words, one string has the standard tension, as when we lightly press the key, we can still hear the correct single standard sound here. This can be explained by the fact that the hammer strikes the surface of one of the three strings, which has the correct standard tension. However, when the hammer comes into intense contact with the three strings there, we can hear that the other two strings produce a difference in sound by ( a minor third) and a (Major second) down and it's all sounding simultaneously.
  
  What can be done DIY now?
  
  1 Call a piano tuner who can fix this issue.
  
  2 If you have a tuning hammer or a tuning lever, set the tip jack slot head on the tuning pin and rotate the handle of a hammer clockwise to moving it. And as result it's action we raise the out-of-tune note to the desired sound 185.00 HZ (F#3) . Use the felt mute (papp) for convenience during the process tuning piano which need set it between the strings there.
  
  3 In some cases, a temporary mute made of fabric or felt can also be used there when you need to play but the tuner of the piano don't came to your home yet.
  
  https://youtube.com/shorts/OVQyKnZwYoc? ... v7l9VEhTXC