soundboard causing buzz?

[Bec and John]

Hi,

A few days ago a buzz developed on my piano when playing a couple of 
notes (E5 and F5). While trying to figure out what was causing it I 
noticed that if I applied a little pressure to the soundboard from 
underneath the buzz would go away.

Though for the next 2 days the sound was gone, so I just figured it was 
one of those strange sounds that pops up for no discernible reason.

Then today, it is back, but worse. More notes and louder.

I isolated the sound to the left side of the soundboard (while facing 
the keys), maybe about midway back, right about where there is a 
hairline crack that doesn't go entirely through the board. Again, 
pressing on the soundboard would help. I looked on top and underneath 
to see if I could spot loose ribs, glue, etc., but nothing.

Any ideas, fixes? Thanks.

- John