[CentOS] resolv.conf rewritten every reboot. How to figure out who and why?

My machine has a static IP, with dhcp and IPv6 disabled. Every time I
reboot, some process rewrites /etc/resolv.conf, including a comment
about dhcpclient. The only package I have installed that shows up in
"rpm -qa|grep -i dhcp" is dhcpv6-client-1.0.10-16.el5, and nothing in
there is named dhcpclient.

I'd like to figure out what software is rewriting this file and why.
man 5 resolv.conf  and man resolver are unhelpful in this case. rpm
reports /etc/resolv.conf is not owned by any package.

At this point, I am as (or more) interested in pointers regarding how
to find the answer as I am in the actual answer. Please teach me to
fish.

mahalo,
Dave