Yesterday I took my K3 to a local friend Aki, JA1NLX who also has K3.
We made side by side comparison and found that my K3 is something like a compeletely different radio.
I left my K3 at Aki's home last night, according to Aki's report today, my K3 has too much distortion on all bands except 20m band.
He guess DSP board is suspicious and he suggested to contact Elecraft anyway.
So, I sent an e-mail to the Elecraft support today.