I posted something here a month ago on the strange, metallic, booming noises that are being reported around the country. As per Linda Moulton Howe in the Dreamland interview posted above, occurrences of these events is on the increase. Reports are coming in from all over the country, parts of Canada, Great Britain, and other places. And in all of these places no plausible explanation has been forthcoming.
I, personally, have not heard anything like this. From the descriptions in Howe's collection of man on the street interviews, it sounds awful. It's most often compared to train collisions... except that the trains are invisible.