[Elecraft] K3 - Interference tone in SSB modulation

[SM5AJV]

Hi!

I have discovered that my SSB modulation is having a interference tone in
the output. A friend of mine has the same trouble with his new K3S. My K3
has serial number 07341.

The tone's frequency is around 1780 Hz and is 25 dB above the transmitting
noise floor measured in RBW of 0.7 Hz, the test was done on 3672.5 kHz LSB.
Testing on 14240 kHz USB the tone is at 1830 Hz and 25 dB above noise
floor. The tone is clearly heard over the air.

The test has been performed with MIC:25 and COMP:25. The tone disappears
when setting MIC:0.
It doesn't matter if I select Front or Rear Mic input.

I have tried to disconnect everything, even the microphone signal and only
key with PTT or XMIT, the tone is still there.

Any clues of what's going is appreciated.

73
Ingo SM5AJV