This strange 6K I have been working on had loud pops when pressing the External to
monitor button and selecting different sources, after all center section caps were
replaced. After changing fets on 23,24,28 cards it was still there. What I did was
remove all the opamps on the 29 card except st1 and st2 to temporally narrow
it down. This has fixed it, so it seems one or more of those other opamps
where somehow "polluting" the whole system. when I have more time I will put
them back in one set at a time and see what the cause was.