kinBG5S

hi everyone. im a newbie here.
i drive a 1992 jap import BG5S hatchback. it was nice to drive and i like it alot.
the car runs well until it reaches 90-100+km/h. there is an audible wind rattling noise, possibly from behind the dash. It was like this since i bought the car 2 years ago, and i thought is just a minor thing and easy to fix.
has anyone had this sortta problem before? or anyone know how to fix it? thanks.