Sounds like something moving about in your loft.
You need to get up there and look for evidence. Death watch beetle larvae will leave evidence of small mounds of sawdust, (frass?), and holes in the wood where they have emerged.
Mice or rats will leave droppings and posibbly urine trails if the floor is boarded or the back of the plasterboard clean. Rat droppings are bigger than mice dropping, (small dark/black pieces of poo), and rats will sometimes leave a greasy type of streak against anything the brush past. Look all around the edges as this is where rodents tend to run but also look around the whole floor. If you have cardboard boxes or loose bedding, such as quilts/blankets etc, examine these to see if they have been chewed or defecated on. Look for chewed up bit of paper/cardboard/plastic and also check any electrical cables that are exposed.
If you find anything but are not sure then take photo's and post on here.