There is a muscle in your ear called the tensor tympani which runs through a tube from your outer to your inner ear. Its purpose is to quickly tense your eardrum to stop it from vibrating whenever theres a loud sound, to protect it from getting damaged. Some people can force it to tense on command, causing sounds to appear muffled for a bit. The tube that the tensor tympani resides in can get infected/full of water, which causes a condition known as swimmers ear.