If you find yourself in a high-volume situation with no ear plugs or other hearing protection at hand, several sources have suggested humming or grunting as a way to marginally protect your ears. Humming activates the stapedius muscle, which stabilizes the stapes, a tiny bone in the inner ear.
Disclaimer: this trick in NO WAY substitutes for proper hearing protection and a steadfast aversion to high volume levels. Always protect your ears, as a musician, engineer, or producer, they are your most valuable resource!