[universenz]

Surely you used several USB Ethernet adapters to rule them out as being the source as well right? Those types of dongles are well known for calling home.

[walterbell]

Good observation :) Multiple ethernet adapters: Apple original (ancient USB2 10/100), Tier 1 PC OEM, plus a few random ones. Some USB adapters emit more RF than others.

[Melatonic]

And your sure it wasn't some built in Apple service ? I believe they host a ton on GCP