[Elecraft] K3 extra xmit frequency

[Bill Stravinsky]

A friend of mine (100 miles away) recently noticed a dual signal being transmitted from my K3 possibly coming to lightsince I went to high power.  The problem has surfaced when I xmit on 40 & 80 (don't know of other instances).  Thereis a duplicate signal 18khz lower on cw, reduced of course but pretty loud.  The first cw character starts out with a chirpbut cleans up after the transmission begins, but still seems like its not a pure signal according to my good friend.
RADIO HISTORY: added the 2nd vfo, synth boards, newer dsp board, newer kio3
also had a K4 tell me I had strong dual signal in a recent contest (not sure but might have been on 20 mtrs)
Any ideas on the cause(s)??
BillK3WJV
p.s. sure would be nice if I had one of my S line rcvrs operating to gain possible causes right in the shack!