A British thermal unit (Btu) is a standard unit of energy that is used in the United States and sometimes in the U.K.
There is another defect in tires that can cause a vibration called loaded road force variance. The tires and pass a visual inspection, a radial and lateral runout test, be perfectly balanced, but still cause a vibration. This is due to the internal defects in the tire.
The sound of the tread contacting the road also causes tire noise. Another factor that causes tire noise is the sound of air that is compressed inside the tread grooves. Diverse tread compounds and tread styles cause different levels of noise.