2006 XC70 wind noise coming from the back
 

I was test driving a 2006 wagon and noticed there was a howling wind noise coming from the rear when at highway speeds of about 60+MPH. I thought at first it might have been the sunroof, but it was all tight, as where all back seat windows. Sounds like its further back, like from the back hatch. I checked the rubber gasket around the hatch and it seemed find, nothing loose/missing. Wasn't sure if it was coming through the up above the headboard somewhere. Any help would be greatly appreciated.