What is the expected daily egress traffic from full Testnet node

I have a full testnet node running on GCP with Parity. After about a week of having it fully synced, the egress traffic from the server spiked substantially and started sending out 250GB per day to random servers around the world on random ports, until I closed the firewall entirely (not sure if these were other testnet nodes, but assume so)

Unfortunately with the firewall closed completely, the node won’t sync anymore.

This amount of traffic seems incredibly high, especially as GCP charges for egress traffic which racked up a $100 bill for three days and the total of 750G total egress.

What is the expected daily traffic that would be sent from a full testnet node?