reply to hardware bum
Re: DHCP troubles OP here with an update:
Well, I found the rogue DHCP server! Turned out to be my Comcast RNG-150 cable box. This box doesn't need to be connected to the network so I just pulled the cable. Now I remember when I got the '150 I saw the ethernet port and just plugged it into the switch in my AV cabinet and forgot about it. Funny thing though, it must have been plugged into the network for more than 2 months before it started acting up like this.
I used netdiscover and dhcp_probe to track this down.