Dejan Corovic
As above, so bellow
Yeah that's an interesting question. They don't create a sonic boom when they leap from a dead hover to hypersonic velocity either.
It is very easy to explain why UFOs don't create sonic boom, just by looking into existing data collected over the last 60 years.
As discussed elsewhere, UFOs are proven to be surrounded by strong electric fields and plasma. Electric field is strong enough to ionize air and once the air is ionized air molecules get repelled away from UFO. UFOs are thus practically surrounded by near vacuum, even when they fly through atmospere. So, that vacuum bubble around an UFO is so large, maybe 20-30 times UFOs own diameter, that when UFO moves air goes around the bubble and there is no sharp point that is needed to start accumulation of shock waves.
I've shown many times before a video where UFO flies through contrail and contrail melts away across whole of its diameter, while UFO is traversing it. And UFOs diameter was maybe 100 times smaller than diameter of a contrail.