[Elecraft] KX1 transmit audio hum/buzz

[Eric Ward]

I installed KXB3080 about a week ago, and just redid L3 with 18 winds.
I had not checked my transmit audio since first building the rig.  I 
just checked it transmitting into a dummy load, listening on my Icom 706 
with a coax jumper as an antenna. 
I have a distinct buzz mixed in with the 600Hz tone.  It is worst on 
30m, but also audible on 20 and 40.  It gets much worse when I re 
install the KXAT1--with the tuner installed, the buzz is louder than the 
600Hz tone on 30m, and also louder than without tuner on the other 
bands.  Current draw is within a few percent of the values suggested in 
the KXB3080 manual; with the display off:
69mA on 80m
47.2mA on 40m
48.6mA on 30m
47.1mA on 20m
I may have had bad audio on 30m forever--I have never had a 30m QSO, so 
no signal reports on that band.  But I do not recall anything but a nice 
clean tone when I tested after I completed the build a couple of years ago.
When I go into tune mode, the power output shown fluctuates +/- 0.3W or 
so (e.g. between 3.2 and 3.5W)--I do not remember it doing this before I 
did the L3 mod--not sure whether this is related to the problem, but it 
seems likely.
I get the same buzz whether I use a 12V linear power supply or internal 
Li batteries.
I have the N0SS zero beat indicator installed, but if I unplug that 
board, it makes no difference, so I am assuming it is not involved in 
the problem.
I searched the list for KX1 transmit audio problems but came up blank. 
Any ideas anyone?
Many thanks and 73
Eric N0HHS KX1 #670