Creaking / Clicking noise coming from wood / cardboard
I hear the same noise and have done in a few houses. After years of chasing sounds round rooms I'm pretty sure the culprit is a tiny brown beetle I've found a few times, 1-3mm max. I'm struggling to identify it. My ex wife could hear it so I knew I wasn't going mad! It can really keep you awake for such a quiet sound! 

I live in West Wales in the UK.