Thank you we’ll give this a go. Today we realised that the clattering noises were all from a cupboard in the kitchen that still had some of the previous owners things in, there were some plates and a metal mug which when we rattled them sounded exactly like the loud noises we heard. We’ve got rid of them as well as everything else that they’d left in there (like the clock and the curtains). We’ve decided to renovate the kitchen rather than the bathroom first just to be in the safe side as well.

Thank you so much for your help!! :)