I can remember being woken up on the narrowboat, by a clang, clang, clang sound, it was quite loud and very scary - perhaps a WW2 mine bashing against the hull - OK perhaps not that likely in the Grand Union Canal. I jumped out of the bunk and searched the boat with the aid of the other friends aboard plus the dog which belonged to one of them. The noise had stopped and we couldn't find anything. Went back to sleep and was woken up yet again by the noise - I grapped the torch which I'd left by the side of the bunk and shone it in the direction of the sound, only to find that it was the dog wagging it's tail in it's sleep and hitting the grill of the (unlit) gas heater.