First check all windows are fully up - kids/adults sometimes only wind windows up till they close the gap but they need to go till they won't go no further. Re seal, there is a strip seal that usually breaks off and falls inside the door - it goes between the inner door sill and the glass. Some keen people retrieve it and somehow glue it back.
"If anyone disagrees with anything I say, I am quite prepared not only to retract it, but also to deny under oath that I ever said it." --T. Lehrer
"The secret of success is sincerity. Once you can fake that you've got it made." -- Jean Giraudoux