What else do you have connected to the Kemper? It sounds it could be like a ground loop issue. Have you tried the ground switches on the back of the KPA?
Also, if you are connected to a computer's USB port, disconnect that too and see if that helps.
ToneDeaf that’s a fantastic point!
I forgot about that but I had that problem for a long time with my old pedal board. In order to program the controller (RJM Mastermind) i used a USB cable from the controller to the computer. I couldn’t understand why I was hearing noise. It eventually turned out to be the USB. If you ste going to have a UsB cable connected it is safest to ise an isolated cable or hub.
Well, I learned my "USB-noise" lesson a long time ago. Kind of an embarrassing story. Used to use a Tascam hard disk recorder from which you could transfer the wav files to a computer via USB.
It recorded with a horrible noise. I figured it is some radio interference, spent a day building a very cool aluminum-lined wooden box for it. Box was grounded, figured the Faraday cage will help. Put the box in, connect again, same exact noise. As I am taking it apart, as soon as I unplug the USB, all noise is gone.
Still have the very pretty and completely useless grounded wooden box 
Try to think larger than noise problem= my Kemper
It can be a ground loop, it can be a problem with the output of the guitar, the pick up, the way you are connected with your computer. For the Kemper well first there is a noise gate you can adjust that you can adjust the input level that .... I had a groud loop before I just switched the AC plug and it was solved. SO you need an open mind try to isolate the problem and yes don't hook up on your computer before you test the Kemper without USB or whatever. Change guitar ... try another on from a friend If the noise is still there then its not the guitar... Test and ISOLATE the problem. And keep you mind open instead of thinking ''its a Kemper noise problem''. Try to think larger and think the problem can be something else too... Good luck. BTW for ground loop it exist product to get rid of that just google it
Well, the OP said that there is noise even without a guitar plugged in.
I assume that the input jack on the Kemper is the kind that grounds itself when nothing is plugged in. So I would still say that the best bet is keep disconnecting things - including using the ground lift buttons - until the noise is gone.
There really should be no noise when the Kemper is plugged into the wall for power and only a pair of headphones plugged into it. No guitar, no output, nothing else. There is no chance for a ground loop, USB interference, nothing.
