My psu has been making clicking noises for the past month now. It happens approximately every 10-30 seconds, both idle and running, but between the intervals, it's completely silent. I'm pretty sure it's simply foreign material in my psu, but I just wanted to make sure.
Clicking can be the fan the psu or as you said an object i suggest taking it out and shaking it to see if its an object. Also a vacuum or can of air wont kill it clean it out. Make sure its just the psu sometimes its a fan get the computer on a desk and use the good old ear and listen.