Yes, this "sonar like" ping has been active for at least a few days. I have looked at it, and I have no idea what it is. It is possibly a channel marker, but if so I don't know why they need it. It continues over the Russian traffic that is sometimes present on that frequency.
It really does sound like a movie representation of an active sonar ping. "One ping only Vasily..."
When not heard on 4649.5 kHz USB, the ping can sometimes be heard on 4397 kHz USB, not sure what other freqs it has been on. Since both of these freqs also have Russian voice traffic, I am not sure if there is any connection there or not.
T!