this is the same experience that I'm having with my '95 Ranger right now. I took it to the shop,and my mechanic put it on a hoist,and got it up to 60 M.P.H.-No Noise!! when I get up to between 15-20 M.P.h.,it sounds like the rear end is out of lube.It makes a 2-tone whirring/howling noise,like something's being run on a turret lathe. Here's the THING>>>about 2 months ago,I installed a tool box,that is mounted behind the cab,and "runs" transverse. About the same time,the "noise" started. I didn't put 2 and 2 together,until about a month ago. I have an extended-cab,and I had a passenger sitting in back. He opened the sliding window,and said that the gap between the tool box and the bed liner was causing the racket. I don't know,but it could be the same scenario for your noise. Just a thought. Hope that's all it is.
