I worked in a semi anechoic test chamber for measuring radiated emissions. We had a few cases like this that one of the engineers was especially good at solvin

I worked in a semi anechoic test chamber for measuring radiated emissions. We had a few cases like this that one of the engineers was especially good at solving. In one, we had a cheaper network switch that was failing one of the limits. One of our engineers walked in with a can of metalized spray paint, applied a single squirt to the inside of the plastic case, and fixed the issue. If you bought one and opened it, you would see a single squirt of silver looking paint on the inside, right where he put his. I've seen a few of these squirts in the devices I've taken apart, so I guess it's not a secret.