PC making click noises randomly?

During usage, my pc just makes audible clicks sometimes. Sounds like a pop or a switch being flipped. There's no pattern, it could be a single click or a couple. Doesn't matter the driver versions, the fans aren't hitting anything and it doesn't affect usage at all. All I know is thay the sound *seems* to be near the back of the pc case. It even clicked when my pc was fully off, wall plug pulled out. Does anyone know what this is? I'm curious.