Probably is the P/S pump . If you have a long screwdriver start listning to pulleys, alternator , watepump ps pump ect. See where its the loudest , If you cant figure it out take the a/c belt off and see if it changes . Just have to narrow it down . Ive seen many 98-99 alts with a whiny engine , Usually center idler pulley,P/S pump or alternator .