Something interesting I just found (searching through logs) is that my ISP was initiating some of these packets. I did a whois on the ip address:

Interesting... Jumpstart?

I had this same problem a while ago (but it was MUCH more persistent) when I put in a new router. There was a setting called jumpstart on the router that I turned off and it help quite a bit...

It took awhile to track it down but it IS a Mac (apple) server mDNSResponder and if you have installed bonjour on your system or have a Time Capsule or other Mac machine this is a very chatty service using ssdp I believe and that service is used extensively by Microsoft products. It is supposedly benign and just watching the nic card with tcpdump or Wireshark doesn't help because the VOLUME is huge. I don't want to block it because I use bonjour so my Linux box can backup to the "Time Machine" as well as XP and my macbook.

http://www.broadbandreports.com/forum/remark,15632024

has some more information, but it is obtuse and difficult to get info otherwise.

Bigtime necro thread. It might have been better for you to open a new thread and reference this one. It's been over 3 years since this thread was updated, until today...its a common habit here to not update threads that are that old. Just an FYI.