I do volunteer work at allexperts.com. A recent question pointed me in the direction of this YouTube video.
Parts of the video seem like a hoax to me. The sound quality of the strange sound seems way better than the thin audio of the background sounds (I listened thru a big stereo). And in once instance, it seems the same unidentifiable sound continues from one video to another.
This suggests someone mixing the strange sound into the original audio track, which is probably what happened for most of the “evidence” here. But the TV segments seem more convincing. So who knows?
Did something really happen, in several locations? Watch and decide for yourself!