Well, I'm back here again!

I'm sure this is a really simple and basic question that you guys see all the time, but it bugs me that it happens.

When I'm pedaling, I hear a small clicking noise that sounds a bit like when a stone hits the frame, or one of my laces are flapping around on metal (I know it's neither of these).

I've tried shaking the cranks and they seem tight - no rocking from side to side and the pedals seem to spin without a problem. I've also noticed that it doesn't do it unless I pedal fairly gently, like if I'm going downhill or waiting for someone to catch up with me.

The pedals are fairly new so I would hope it's not them.

Can anyone suggest what this may be?

Thanks,