Uh, find the piezo beeper and disconnect it...
But really, this is happening because you removed the old Airbag. I may be pulling this out of my ass, but most cars have sensors that tell you if the airbag is messed up, and alerting you if that is the case. You're car is telling you "YOUR AIR BAG WILL NOT DEPLOY IF YOU GET CRUSHED BY A SEMI".
Want it to stop? Put the old wheel on, or one with an airbag.