Bit of a schoolboy error on my part, just thought I'd share for any other users if similar issues.
A recent thread on connecting the Kemper to amps etc emphasised using the correct cables. Fairly recently one of my guitar cables had broken, so I just grabbed a brand new TS cable I had in my drawer. I noticed I was getting a lot of static type noise on note decay and reverb tails, which was driving me mad, I was messing with noise gates and getting frustrated thinking something had gone wrong with the Kemper. After reading the aforementioned thread a dim bulb lit in my dim head..
Looking at the cable it was a microphone TS cable. So, not all TS cables are equal!
I dug out one of my old guitar cables I use for gigging - hey presto, don't even need a noise gate now for most profiles I use.
TL;DR use the right cables / leads