When two notes of nearly equal frequencies are sounded together, a periodic rise and fall in sound intensity can be heard. This phenomenon can be called

Answer Details

The phenomenon described in the question is called "beats". Beats occur when two sound waves of nearly the same frequency interfere with each other. The interference causes the sound intensity to periodically increase and decrease, creating a pulsing or beating sound. The frequency of the beats is equal to the difference between the frequencies of the two sound waves.