Im using the 1KFA with my Flex 6300. I noticed the same phenomenom as you - kind of an electromagnetic hum / buzz - I put it down to the the transformer in the SPE sucking up all that current at 44 volts to feed the power transistors.
I found the bigger annoynance to be the gale force fan noise kicking in at 65C - I have now built a virtually sound proof closet in the shack - immedeately to the right of my desk , to host all the gear including the 6300 and PC . As the closet it so close I havnt needed to extend any of the usual standard leads (USB, tx key, VGA etc). All heat is sucked away by a very quiet extractor fan and an inlet vent for cool air at the bottom adjacent to the linear :o)
When I key up or the fan kicks in now a enjoy virtual silence - no PC noise either which is awesome !
I was also annoyed by the fan noise (also the case with the flex 6300) on the SPE Expert 1k so I went ahead and bought online quieter fans. Changing the front and back ones was a piece of cake. The fans use the same two prong female connector as the PC chassis fans. There are a couple of fans inside which require a bit of disassembly to get to them, so I left those there. I was able to greatly reduce the noise. You can find the fans in computer online retailers such as newegg.com
I also noticed something with the new version of DDUtil.
I do not need to use the Slave COM1 trick to have the Expert follow band changes.
I selected RS232 instead of FlexRadio for CAT in the amplifier and select "Amp Follows DDU PTT" and "DDUtil Follows Amp PTT" in the AutoDrive setup menu of DDutil.
Not sure how it happens, but it is definitely DDUtil sending the Band change info back to the SPE Expert 1k amp. Anyone else noticed this behavior?
Enjoy the amp Larry, it is a fantastic piece of equipment. 1Kw amp, 4 port antenna switch, 4 antenna auto tuner, SO2R, two transmitter switch, remote operation and digital Power and SWR meter all in one box.