For some reason, since around midnight last night, there was a ton of broadcast traffic on our res-hall network. Around 150KB/s in fact. It was enough that wireless in my office was mostly unusable.
Using tethereal I could see almost all of the traffic was coming from 2 MAC addresses and it was broadcast ARP traffic asking who has 192.168.1.1. I don’t know why 2 computers on our network decided to do this at almost the same time, but disabling their 2 ports solved the problem for now.