I have the same noise, and it's been like that for the last ~10,000kms and hasn't got worse (or better). It just seemed to start one day out of the blue. The noise on mine seems to come from more towards the rear of the car. I also get a horrible shudder when going downhill and letting off the gas in higher gears.
I've been collecting parts like wheel bearings, driveshaft carrier bearings, UJ joints etc and will start replacing items one by one and see when the noise goes away. It could also be the rear diff (or AWS pump for that matter).