A sound that does not change pitch with road speed, engine RPM, etc? Sounds like an electric motor, such as an HVAC fan motor or fuel pump. What I can't explain is why it stops when you are stopped. Sometimes the alternator voltage can drop a bit at idle if there are other loads going on at the same time. That might affect the noise of a motor. I'd start by changing the HVAC fan speed and see if that changes the sound, or possibly a different setting on the air direction to defrost or dash vent only or some other setting. Possibly the stepper motor on the blend door? Then maybe try energizing the fuel pump motor without the engine running.

 

rxjimmy, Thanks for stepping up to help me with this. All your logic sounds good. I too thought electric motor, but it's too loud. Not loud but too loud for that. That symptom, "stopped when I am stopped" just screams "wheel bearing" to me. It'll be hard for me to test for that. My hvac system was clear down until I put in a new blend door activator. (Twas the broken gear.) So it ain't that. The fan quit also. Dead. Fuses etc were good. I'm a bit hesitant to say this but I wiggled wire plugs and actually gave the plastic hvac housing under the hood a dozen heavy whacks both to try and jar something loose and for a bit of joy. When I turned it on then a big cloud of dust blew out. It works good now, manual and auto both do just fine. It was suggested that I look for a warm hub to find a wheel bearing fault, but they all felt cold actually. Ten miles to warm up. I keep thinking it would be a front wheel bearing. (It's 4wd) Is it safe to assume that it's the front? Do the fronts go more often?