[Elecraft] K2/100 output power fluctuation

[Ken, KA0W]

Hello! 

I'm noticing a power output fluctuation of about 10w on an external Array Solutions digital wattmeter and on an analog wattmeter out of my K2/100 (sn 6384). 

The load isn't changing, tried different dummies, coax, and antennas too. Past recent history of station - no load problems thru 1.5kw.
 
It is more of an output jump, up and down - continuously back and forth. A fast jump, near instant. Doesn't matter much about power setting, whether 30w or 100w. 
 
At the 10w level (PA not switched in) out fairly stable, no jump up and down jumping. 
 
When using the 20w limited tune initially starts at about 27w than drops to about 18.5w and remains there - no jumping.
 
When bypassing the 20w limited tune (holding Display and Tune)  I get the jumping.

RF getting into a  K2 sensing circuit that controls output? 
 
Another possibly related problem is thumbing noise in computer speakers. I have the audio running into the computer. At power levels 10w and under no thump. 11w and above (PA switched in) there is a thump. Computer is otherwise RF proof from QRP thru 1.5kw, no problems with many other rigs and setups.
 
Book measurements and performance outside of problem listed above are excellent. Receive is outstanding, amazingly quiet on 40m and 80m. 
 
Anyone with similar K2/100 history ? Suggestions?
 
Thank you for any and all help.
 
Ken, KA0W