It’s not static. Most likely one of the following:
Loose solder joint anywhere, not necessarily just in the signal path. A transistor or diode from the power supply rail to the input or driver stage being cut off will intermittently cut power and also cause "static" noise.
Broken component leads, especially voltage regulators and transistors that have heat sinks attached without the sinks or the device being independently supported off the pcb. This is a common cause of split leads at the pcb and is similar in effect to a bad solder joint.
Damaged transistor insulators. If transistors are removed and the mica insulators are reused, there is a chance of them cracking as the transistors are removed or screwed back in.
I always start by reflowing all solder joints because sometimes it’s difficult to spot a bad joint. 9/10 it fixes the problem.
Loose solder joint anywhere, not necessarily just in the signal path. A transistor or diode from the power supply rail to the input or driver stage being cut off will intermittently cut power and also cause "static" noise.
Broken component leads, especially voltage regulators and transistors that have heat sinks attached without the sinks or the device being independently supported off the pcb. This is a common cause of split leads at the pcb and is similar in effect to a bad solder joint.
Damaged transistor insulators. If transistors are removed and the mica insulators are reused, there is a chance of them cracking as the transistors are removed or screwed back in.
I always start by reflowing all solder joints because sometimes it’s difficult to spot a bad joint. 9/10 it fixes the problem.