Oh yeah, hedgehogs are nocturnal animals in case you didn't know already. I woke up at 2:30am to his running wheel making a clanking sound. It's a "silent wheel" so something was up. Was it making the plastic cage wiggle and make that sound? Was it the floor of the HOL making that sound? What was it?!?
I had to get up to investigate because I couldn't sleep with the occasional clanking. (Niko is so cute when he runs btw.) I lifted the plastic cage out of the HOL - still made clanking sound. I inserted some bubble wrap between the wheel and the side of the plastic cage - still made clanking. I unmounted it from the cage and put it on it's stand - still clanking!
So, by this time I woke up enough to have my engineering mind kick in to solve the problem. See that yellow knob in the middle? It's hiding a screw. A screw that apparently was loose. I tightened the knob a little by hand, and voila! No more clanking! I can sleep!