Hello there,
I just joined the site. i have a simple setup -beocenter9000 -beogram5000 -penta6603 mk?
i got/Had the same problem:
I dismantled (4 nuts n washwrers on the bottom do it all! dont loose them. lay onto a bunched towel and loosen in rotation.) and found loose/bad connections, after cleaning and reassembly it worked fine.. Then! the other did the same nd got worse fast then crapped out!. I took it to a genious and he said it was all good just a smthin small problem. note when you re-assemble those 4 crews back finger tighten only work on rotation and wobble the base on gently as you do, then a 3/4 turn only! with pliers!
still popped and crackled at extended low volumes!! so for some reason i tried making sure i was only set to link which helps. finally i placed the speakers very far from each - i did this only to use the very large volume of funky cable without any bunching thinking there was feedback or something. this workd great no popping or cracklkeing if not in use the speaker/s shut down to orange but after activating and unplug-repluging there great again.
your problem might, might?, just be bunched cables? what kind are they. do your Penta screens work?
G