Did you try this:
$args = array(
'post_type' => 'attachment',
'posts_per_page' => 5,
'post_status' => 'inherit',
'post_parent' => $post->ID,
'exclude' => get_post_thumbnail_id( $post->ID )
);
Did you try this:
$args = array(
'post_type' => 'attachment',
'posts_per_page' => 5,
'post_status' => 'inherit',
'post_parent' => $post->ID,
'exclude' => get_post_thumbnail_id( $post->ID )
);