You should check man csh on your system to be certain of the sequence of "." files fired when your shell starts.
From memory, for c-shell it's a system .login-type stored in the /etc (maybe /etc/cshrc). The different Unixes may vary in the sequence, but I think it's supposed to be system "." files, usually followed by private "." files in order to overlay generic system values with private, or group settings. Typically, for every "private" dot file necessary to the shell startup, there's a corresponding system-wide generic supplied. (If nothing else, the system-wide copy serves as a template for the SAs to set up new account of that shell type.
Since you mention DISPLAY, I'm assuming you're also doing X Windows, so you also have to check private and public .Xinitrc, and (I think) .xstartup.
Sorry for the long messege, but there's all sorts of places your "DISPLAY" could be hiding.
Hope this helps.
Hutch