This is just conjecture, but I think tinnitus is caused by vibration of the inner ear that doesn't come from the eardrum. The inner ear is designed to be resonant for audio frequencies, and the earplugs contain them, maybe too much. Just N=1 longitudinal study involving an early stage career and now way too much podcast listening. Covering tinnitus doesn't make it better. Covering the 'noise' is futile. The best you can do is try not to make it worse. You'll never get relief. But you can achieve surrender.