[syMPh]

Hey Musicman, I had one machine which I upgraded by putting a fresh install of High Sierra on it. The other machine has been left as it was on Sierra. The only thing which has happened is I took the Sierra drive out of the "clean" machine and used it to booth the high Sierra machine a few times while I was trying to get high Sierra sorted out... I don't know how that could have done anything to either but I also have a old mountain lion drive which if used to boot all these audio errors aren't evident. so I might just go and reinstall a new high Sierra on a fresh drive and see if that fixes the issue... Thanks very much for chiming in with all the suggestions guys :) cheers