annoying sound

We have an '03 expedition that makes a annoying sound that seems to come from the tires, maybe. It's a "woo woo woo woo" kind of sound. It's was making this sound when we test drove it so the dealer "fixed" it but it's back.We just got an alignment and balance but that didn't really help. Is it the tires or something else. Can't tell if it's coming from the front or back.