rimfire

I have a 05 GT and at 4500 miles the rearend spun the bearings and gald the clutch in the limited slip rearend, i was told after inspection. My local ford dealership replaced the whole rearend ( except the axles). Now when i reach 30+ mph and all the way up to interstate speeds you can hear what sounds like sucking air from the rearend. I know that sounds stupid but it doesnt sound like a whine more like pulling air thru your lips.It is not really loud either , but it is there. I was just wondering if anyone has a similar noise in their rearend and would like to hear opinions. maybe i am just paranoid, maybe it was supposed to sound like that from the start. thanks