It may be somewhere like '/usr/lib/perl5/5.8.8/CPAN/Config.pm' .. I think maybe older CPAN was using the ~/.cpan dir or something with config- not certain about that. The default config can be overridden with ~/.cpan/CPAN/MyConfig.pm (see below)

Try # locate CPAN | grep -i config

Here is one of mine (/usr/lib/perl5/5.8.8/CPAN/Config.pm), in case something really different stands out..

# This is CPAN.pm's systemwide configuration file. This file provides
# defaults for users, and the values can be changed in a per-user
# configuration file. The user-config file is being looked for as
# ~/.cpan/CPAN/MyConfig.pm.

$CPAN::Config = {
  'auto_commit' => q[1],
  'build_cache' => q[10],
  'build_dir' => q[/root/.cpan/build],
  'cache_metadata' => q[1],
  'commandnumber_in_prompt' => q[1],
  'cpan_home' => q[/root/.cpan],
  'dontload_hash' => {  },
  'ftp' => q[/usr/bin/ftp],
  'ftp_passive' => q[1],
  'ftp_proxy' => q[],
  'getcwd' => q[cwd],
  'gpg' => q[/usr/bin/gpg],
  'gzip' => q[/usr/bin/gzip],
  'histfile' => q[/root/.cpan/histfile],
  'histsize' => q[500],
  'http_proxy' => q[],
  'inactivity_timeout' => q[0],
  'index_expire' => q[1],
  'inhibit_startup_message' => q[0],
  'keep_source_where' => q[/root/.cpan/sources],
  'make' => q[/usr/bin/make],
  'make_arg' => q[],
  'make_install_arg' => q[],
  'make_install_make_command' => q[/usr/bin/make],
  'makepl_arg' => q[],
  'mbuild_arg' => q[],
  'mbuild_install_arg' => q[],
  'mbuild_install_build_command' => q[./Build],
  'mbuildpl_arg' => q[],
  'ncftp' => q[/usr/bin/ncftpget],
  'ncftpget' => q[],
  'no_proxy' => q[],
  'pager' => q[/usr/bin/less],
  'prerequisites_policy' => q[follow],
  'scan_cache' => q[atstart],
  'shell' => q[/bin/bash],
  'show_upload_date' => q[0],
  'tar' => q[/bin/tar],
  'term_is_latin' => q[1],
  'term_ornaments' => q[1],
  'unzip' => q[/usr/bin/unzip],
  'urllist' => [q[ftp://cpan.pair.com/pub/CPAN/], q[ftp://carroll.cac.
+psu.edu/pub/CPAN/]],
  'use_sqlite' => q[0],
  'wget' => q[/usr/bin/wget],
};
1;
__END__
[download]

Also, I am assuming you are running as root.. look inside ~/.cpan/CPAN/MyConfig.pm, is that file there? Anything strange?

And you did mention you looked inside ~/.bashrc and there's nothing freaky.

Maybe also compare the test and production machines cpan configs (against each other).. and their env set variables ( with '# set' ).