Ford Ranger noise .high pitched whine/hum
Just bought my first Ranger today. A 2006 2WD XLT Automatic 5-speed with overdrive and cruise control. Has under 19 K miles. Looks spanking brand new; not a scratch or dent and beautifully detailed. However... ( ! ), I notice a high pitched whine or hum at hiway speed (well, above 30 mph) which disappears when I take my foot off the accelerator. At first, I thought it was tire tread noise until I let it 'coast' a bit. (Noise disappears when coasting, returns when I put foot back on the gas).
Ideas what to look for?. Does not seem to be on only one side, either front or back... just "underneath somewhere". Am I just being picky? Is this sort of noise normal for this vehicle? I am a newbie with pickup trucks.