Todd assists individuals with these issues more often than I do, however also don't discount the possibility of a malfunctioning PHP script. If you recently changed a PHP script, it may be malfunctioning to the point of causing a core dump. I know myself, at one time I built a PHP script at one point which frequently requested data from external URLs and the script generated core files routinely.
While the server will continue functioning, I would recommend investigating possible causes for the core files so they do not fill up your disk space and so you can fix whatever is causing these issues in the first place.