updated thought it was only from one side but it turned out to be from the driveshaft.
Just started today. When in motion I get a squeak or squeal from somewhere along the passenger side that sounds almost like a bad belt (it’s not) that raises in volume with speed and decreases when slowing to the point where if under 5 mph you won’t hear it. It’s not effected by braking, turning, or RPMs. My suspicion would be bearings but I’ve never heard bearings squeal, only roar. I’ll test it myself tomorrow, but is there a chance it’s E-brake related? I just did a clutch job and had to remove and reinstall the arm for the E-brake while I did it.
More info: 66 Mustang, 200 ci, Manual trans, 9in drum brakes, power nothing.