Scratching noise

hi, my PC has recently been making a scratching/clicking noise, I'm not sure how long it's been doing it, but I have just noticed it now.

I immediately thought it was the HDD, and removed the side panel to listen close, once I took the side panel off, it stopped. When I place the case near the pc, the clicking stops, it doesn't even have to be completely attached. I can have like 2 inches between the side panel, and it being secured, and the clicking noise will start. The fans are definetly not hitting it, and I dont see any wires or anything touching the fans.

Is this just a normal noise all pc's will make, and I'm just noticing this now, or is something up?

It does not make a sound like something is hitting something, as it gets quieter and louder, sometimes stops completely for a few seconds,