When it comes to describing loud and unpleasant sounds, it's important to have a wide range of vocabulary at your disposal. While "most ear-piercing" may be an effective way to convey a high level of discomfort, there are plenty of other antonyms that can help to paint a more nuanced picture. For example, a sound could be described as subdued, muted, or even soothing in contrast to how piercing it may be. Soft, gentle, and mellow are also adjectives that serve as antonyms to "most ear-piercing." Ultimately, choosing the right antonym will depend on the specific context of the sound being described.