I have long had issues with hum in my house. Had a guy come and check the ground - and the connection is apparently good. I have A/C units that cause noise when turned on - that is the major culprit, and my computer also gives out sound. All my guitars get the same high-pitched hum (including humbuckers but less so).
The ground lift on the kemper changes nothing.
I have read about DI boxes with amps removing hum - but wouldn't it be doing the same thing as the kemper's ground lift?