EKO SC800 solid state amp crackles

[spy]

I serviced an old EKO solid state guitar amp and it has this unusual problem. It crackles in random time. Sometimes it's loud and sometimes it's like radio interference or better, static noises. Sometimes there's no any crackle at all for an hour or so and then suddenly it starts again.

I refreshed all the solder joints, even replaced a lot of resistors and the differential pair transistors but the crackles are still there.

I have disconnected the preamp's signal from the power amp pcb and still there, I guess the problem is at the power amp.

Unfortunately, I can't find any schematic to help you out. What exactly is this? A joint/solder? A component? Capacitor? Diodes? Any of these? I haven't replaced the rectifier diodes, yet. Do it immediately? Let me know what do you think before I start to replace everything.

[52 Bill]

What exactly is this? A joint/solder? A component? Capacitor? Diodes? Any of these?

Any and or all of the above.

When the noise happens, is there any measurable disturbance to dc voltages?

[spy]

I didn't check the dc voltages as the noise is very random and not for a long time but I'll try to do it.