98 Legacy Outback noise at 60+ mph

[palfer]

Hi everyone! I have a 98 Legacy AWD with 45K. She has a loud noise when I reach 60 mph. It's not a grind, more like something vibrating in wind so to say, but it is very noticable. If I let off or press down more on the gas the noise with go away for a few seconds then re-occur. It hasn't affected the performance (yet) but I'm concerned about continued driving like this. I've been under the car and cannot find anything loose (exhaust, underbody, trans, etc) Any ideas you folks have would be appreciated.

 

thanks again!