[cadgear]

I don't think it'd be the MC, if anything it'd be the booster. But I imagine it could be the rack, the PS hoses connect there I think. Though I'd imagine you'd hear the Power Steering pump make noise before the rack if its just at idle.

Try to pinpoint it using a long handled screwdriver or a broomstick put to your ear. Listen for where the noise is loudest.