You're being hit with multicast traffic from someone else on your OptiComm node. OptiComm services are layer-3 resold services (which means iiNet don't control the network at all until it hits their point of interconnect with OptiComm for a given state). All OptiComm connected houses in an estate share a single layer-2 network; chances are some moron's plugged their laptop directly into their OptiComm NTD or has done something else stupid to flood the network with broadcast traffic.
The good news is, this makes absolutely no difference to your connection whatsoever, and OptiComm have probably noticed and will be (very, very slowly) working to fix it.
The bad news is that unless you can identify the source of the traffic and tell your EdgeRouter to firewall it, there's probably nothing you can do.
Call the iiNet support line and have them call the Fibre team to lodge a fault with OptiComm if you really want, but all that'll probably do is make Opti charge you a fee for reporting a fault where there's no fault.
I worked at ii for over a year and dealt with all kinds of dumb crap from OptiComm connected services. Good luck!