PALATINE

I have a JDM MY97 Forester fiited with a Apexi SAFCii, Dawes MBC(1 bar) and AFR meter , a HKS FCD and a knocklink
everything is fine when driving steady and hard
but when it gets marmed up if i stop and leav it running the SAFC starts reading slight knock first 2-3 then the longer it sits ticking over the worse it gets though rev it even slightly and the knock stops registering but the knocklink doesn't read anything. the Safc seems to take the last reading and add it to the next on it got upto 18 on tickover and 14 when driving or revving last night it all very strange but I guess hat I'm asking is is this knockin gat tickover of 3-4 any thing to worry about as It's not audible at all and its not even lighting up the 2nd green light on hte knocklink?
PS its fine today from cold untill it get warm and then starts again
and its not got piston slap, it also had a new crank and bearings 12 months ago