Hi Volvo afficianados. This is my first Volvo and first posting. We got a used 850 Turbo wagon for my daughter to drive to college, so we wanted something safe. It's a pleasure to drive for a ten year old car. A week ago, we began hearing a humming sound, perhaps best described as someone blowing on the top of a bottle. It's hard to pinpoint where it's coming from, but it seems like the rear. It seems to occur when we go over 40. The temperature here has been pretty much summery, so I don't think it's outside temp related. It occurs in and out quite early in a trip. At first I thought it was a wind/ventilation issue, but I'm convinced it's more than that. A couple of weeks ago we replaced the front brakes and rotors. All fluid levels are ok. I'm well aware I have a finicky car that can cost a bundle to upkeep. There is an indy Volvo specialist in the area, but perhaps someone may give me a few thoughts before what might be an expensive process if the right diagnosis isn't made. I'm not great about knowing what's what to fix, but I'm willing to try before I call the Volvo doctor. Thanks so much!