I see from your other question that you are running HP-UX. Is the source quench coming from an HP-UX 11.0 box? 11.0 has some problem reqarding source quenches and you need to install the latest patches.
A "source quench" is an ICMP message that is supposed to come from a router that has been overloaded. It's not really used much and anyway a host was not supposed to send them.
Actuall I had put this HP-UX machine system to reboot & was continuesly pinging from my local windows desktop to check whether this system has come up or not.
When the HP-UX system started comming up initially I got the Quenching reply & after some time in started replying normally.