strange digital clipping

hi,
I'm a very happy owner of a KPA PowerHead, but in the last week something strange happened...
In facts when I play guitars with single coils KPA sounds great as usual, but when I play guitars whit humbukers through it I can hear like a digital clipping come out on every distorted profile (by now I use only factory and MB profiles) except for a profile that I found yesterday on rig exchange...
Input and output are not clipping, anyway I try to reduce clean sens, dist sens and rig volume but nothing change. I try It with several humb equipped guitars and many cables, either in the front input or the alternative but it always sound this way.
Has anyone had similar experience and knows how to solve the problem?

I tried monitoring it through the headphones out with a couple of headphones model, with a real cab, and with the main out (either trs and XLR) through a couple of different audio interfaces
Mm no the cab simulation is off only on the monitor out
And yes the problems is only with the humbukers on distorted rigs except for one

Input sense is sets to 0 and also the dist sense
I tried to tweak them in various amount, but the problem persist

Ok, I'll do it tomorrow
Thanks

hi, this morning I met a friend of mine who has a KPA for a longer time than me...he suggested a system reset...
now everything seems to be OK and KPA sounds amazing also with my Humbuckers equipped guitars
anyway thanks so much for the support