lightning storm

Yes, it is probably EMI either entering directly into your system or EMI affecting your power lines.  In any even, it is better to turn everything off during a storm.  Even better is to unplug the gear because a direct hit of lightning could be powerful enough to jump the switch in your gear.

Even when lightning does not directly strike a power line the magnetic pulse is picked up by every cable nearby, from high tension lines to your house wiring, antenna cables and Internet provider's wiring.  

We don’t always know when a surge will come down the line so having a good surge protector is essential IMHO, but even then I would absolutely recommend unplugging when you know a big storm is coming through.  Sometimes I even turn off my HVAC and range as well, despite having a whole house surge protector.  

Thank you for your responses. Much appreciated and I will be turning everything off and disconnecting in the future.

How is "electronic rust" detected and repaired?

Storms can cause slight shifts in ground potential, which may temporarily aggravate grounding issues, causing hum or static. If you only heard static during a storm but it went away afterward, it was likely due to temporary EMI or line noise.

BTW, Electronic Rust has nothing to do with lighting or thunderstorms. It is an informal term often used to describe corrosion or degradation of electronic components or circuit board traces, typically caused by moisture, oxidation, or chemical contaminants. It’s not actual rust (iron oxide), but it behaves similarly by slowly damaging the delicate metal pathways that allow electricity to flow.