Train causing static electricity discharge?

We live right above the LIRR tracks in Rego Park, Queens. Sometimes in the morning when a train goes by, we see a bright flash of light accompanied by a tiny pop, like a static electricity spark, but much bigger. It also seems to be coming from inside our apartment, right by the wall near our radiator and air conditioner. There weren't any burns or ozone smell afterwards, just this bright flash and pop and then nothing. And it doesnt happen every time a train goes by, only sometimes. Is it possible the train is doing this somehow? More importantly, is it dangerous?