I have a similar problem. Somewhere on our network there is a RAS that's bugging my SCO UNIX box every few seconds. The result is the bootp program filling the syslog with error messages about a bad address from this MAC address. The address is 52.41.53... and that's a RAS. But I can't find this offending device by the MAC address.
I found some software that hunts down all the MAC addresses on my subnet, but no further.
Any suggestions?