Had a similar sound coming out of my 98 2.5.Sounded like air whooshing out at high rpm,was louder than the engine.Took it in they found,a hose that had come off the cat,or so they said.Anyways turned out that it blew off two days later, was traced to a plugged rear precat.Had the cat replaced under warranty thank god,and has been fine since.
Good Luck.
