What's this moan?

Hey there,

So, again I’m asking myself: What does this moan mean, you can hear sometimes when attacking an enemy? It’s most noticeable when attacking several enemies at once, since it seems additive in volume.

I checked for a video sample to demonstrate:
For example, check this out at 3:49.
You can hear it every second (until next mob is encountered).

Does anyone please know what it indicates? Asking myself since day 1.

In the video, it is the Haunt skill from the Haunt relic. Each time it deals damage (and possibly reapplies the fumble/impaired aim if I am not mistaken) it makes that noise.

The damage is not only on cast, but each second.

Thats right.
But any attack is able to invoke exactly that sound on the enemy. So it must stand for sth more general…