Sorry for such delay; this isn't my usual forum haunt. But, if the noise is present while gassing it in park, I don't actually think it would be the transmission... perhaps the flywheel or fluid coupling, but in park the gears shouldn't be moving - there is a little lever that physically catches the tranny gears in [P]; that's what keeps you from rolling on small inclines. Any thoughts on front vs rear of transmission?
Unfortunately, I don't know enough to diagnose your noise much more than this... You can check out Subaru Legacy International
, or perhaps SubaruOutback.org
as other forums that'll answer some questions about the '98 Legacy platform. Moving into conjecture, a whine might be a pressure leak of some sort, vacuum or fluid... or maybe slight mechanical rubbing as parts warm up or expand.
And I've just reread your post. Can you detail what you mean by "jumping from stopped"?