[Elecraft] 10 meter SSB audio distortion

[Andrew Catanzaro]

I get excellent audio reports on my K2 audio on all bands but 10 meters.
People tell it sounds like RF is getting back into the radio.
I have the KAT100 tuner and an RF Works isolator that should prevent RF 
from getting back into the radio, and the K2 itself is gorounded.  The disortion
is present with the Heil H-5 microphone element as well as the MH2 mike and the Heil 
boom mike for the K2.  It happens at all settings of mike gain and/or compression. 
It happens with or with out the KP100 amp in line.  The distortion is present at all power levels 
and when the radio is driving a dummy load.

Suggestions?  

Andy W9NJY
K2 serial number 2651with all the A->B mods.