Sudden tuning instability in Kawai KG-1D c. 1985

[Dave Smith]

This is a nice Kawai grand which I have tuned since 2003.  It has a working DC system (dehumidifier only - this is SW FLorida).  It has been between 2-10c flat each year  when I arrive for yearly tuning. 
  
This year after 5 months, the owner called me for another tuning.  He mentioned that he hears very faint wood on wood creaking sounds sometimes at night from the direction of the piano.  Also, this time the piano was 10-15C SHARP in bass and tenor, and 10c flat in Treble.Is it likely that the plate is rotating slowly clockwise for some reason?  That is the only explanation I can think of that explains the creaking and the sudden instability.  What do you think?  I havent tightened the plate bolts in the last couple of years, since the stability was good.

I did "frisk it for rodentia", as Ron N suggested when I posted the question about strange sounds a few months ago.  No Ro.

Dave Smith
SW FL
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