How can I 'capture' what is doing this to my network?

[NetGobbler]

https://i.imgur.com/2Szt0iw.png


The insight tool I've found to be really good but I can't isolate a time window, just a date window.
I know this is something inside my network, my smokepings to all external sources are showing this blip.
I don't recall installing anything (but I'm sure it was me)
I have too many devices and one of the reasons I switched to opnsense, was to learn how to capture this kind of stuff.

Any tips? 

(note I don't want to "capture" the data, I just want to know which device is doing it, to which destination, to begin with anyhow)

[Obeng]

I think you should check out ntop. You can get a lot of insight on individual connected users, their traffic and a whole lot. Hope this helps