When you close your eyes tightly or yawn, you may hear a low roaring sound in your ears. This is caused by the tensor tympani muscle in the middle ear, which dampens loud internal and external noises to protect your hearing. Some people can voluntarily contract this muscle and hear the sound. It also helps reduce the noise from chewing and shields the ear from damage by muting certain loud sounds, though it can't react fast enough to sudden blasts.