[ILUG-BOM] Ubuntu 11.04 LAN Data Transfer

On my Ubuntu 11.04 install on laptop (amd64 arch) as well as desktop (x86 arch) on the office wired LAN (Intranet, not connected to internet), there is a constant 6-15 kilobytes/second data down happening. The LAN works normally at all times, but even with no activity this data down is running. I checked with internet connected wifi on laptop and a USB dongle on both, but there was no such data transfer in idle conditions. It doesn't happen when on Windows 7.

Is there a tool to find out which port or software is taking this data? I tried netstat but couldn't make a headway. Searched on ubuntuforums but found nothing close enough. Can somebody please guide me how to go about it.