the obvious solution (though not best) is to edit xhld[x]_feed.html in the template manager, replacing all instances of:
<{if $items[i].guid != ""}>
with:
<{if preg_match("/^http:\/\//",$items[i].guid)}>
although personally, i don't understand why you couldn't just eliminate $items[i].guid and just use $items[i].link instead. seems like a lot better solution to me. is there a situation where the guid is a permanent (absolute) link but different than the link?
peace