I'd change CARP, as this is very easy:
In carpinc.php FIND
PHP Code:
} else if ($this->insidechannel==2) {
switch ($this->tag) {
case "TITLE": $this->ctitle.=$data; break;
case "DESCRIPTION": $this->cdescription.=$data; break;
REPLACE that with
PHP Code:
} else if ($this->insidechannel==2) {
switch ($this->tag) {
case "TITLE": $this->ctitle.=$data; break;
// case "DESCRIPTION": $this->cdescription.=$data; break;
Done. This way you can get rid of the notice on your side without having to change the RSS itself.