Now, some of you may think it's because I have been recently bereaved BUT....
1/ It has been going on since before dd died
2/ My dd was only 7 weeks old so didn't do any running about when she was here
dh has heard it, I have heard it and now my Mum, who has been staying with us for a couple of weeks has heard it. At first I though it was our boys but when checked, they are tucked up in bed, fast asleep and they don't look as though they are feigning sleep. It definitely sounds like a child running, as opposed to mice/rats.
Oh and our house has only been built 11 years and we are the only occupants.
Any ideas?