I'd suggest looking in the web.config for some sort of rewrite rule. If there is nothing in there, then look at any custom aspx master templates to see if there is a redirect in there. If nothing there, look at any custom webparts which might perform a redirect that could be placed on a master page. Look in the site's domain aliases for a localhost alias and see if it has a redirect on it.
There are about a dozen or more things to check but I'd start off with those first.