Geez Allicloud, that sounds creepy :!!
Not that I don't believe in paranormal activity (everyone here probably knows I do

), but have you been checked for tinnitus by any chance? I've had it since I was still a little kid, and sometimes I hear a thumping noise that lasts a few minutes and grows louder and louder. Again, I'm not trying to disagree with you. I'm just curious, because before I found out it is tinnitus, I thought maybe it was psychiatric

.
As for me, I was recently out in my back yard with my dog. It was a quiet morning, and I was out there pulling weeds while my dog was laying down near me and napping. Just then, about fifteen feet away from me by my fence, I swear I heard a human voice go, "Psst! Hey! Psst!" in a whisper. I looked up and saw nothing and heard nothing else. Then, I heard footsteps running, and then my dog jumped up and started barking like his alarmed maniac self while staring at where the voice had come from. The entire time, there was nobody by or on the other side of the fence :!. Spooky indeed.