[Elecraft] RF feedback? only when using KXPA100

[David F. Reed]

This did not used to happen; it is new to my set-up, nothing I am aware 
of has changed...

When trying to operate JT65, if I set the power to 10 watts, everything 
is fine (KXPA100 is not active).
If I set to anything above 10 watts (yeah, like 11 watts or more), I get 
bad RF feedback (sounds like motor boating in monitor).
SWR via tune looks good, all cables have been taken out, checked and 
re-inserted.

I am stumped and looking for hints as to what I ought to look at next, 
or re-check or try.

Thanks & 73 de Dave, W5SV