biological sonar is the combination of generating and gathering sounds in the ultrasound spectrum to create imagery. No matter how good the "software" is, the further away something is the more distorted the image will be. The ability to sort sounds based on source can easily be rather overpowered. Sorting based on wavelength is more plausible. But even then, loud noises will be disruptive, even in unfocused wavelengths. Even the best ear can't pinpoint the source of a sound if it has bounced a couple of times. The angular mathematics needed to calculate such are too extreme for anyone other than super geniuses to be capable of.

Thus, while one could theoretically get an image of where someone is through echolocation, it might have minor deviances. More importantly, though. How would he have learned how to aim at such a distance? A degree or three off, and the arrow misses by a considerable distance. Unless he constantly gets new images, with accuracy, he would have no proper means of knowing exactly where he is aiming with a bow. A throwing knife (or similar) on the other hand, is held in the hand. You know at all times exactly where your hand is, even in absolute darkness. You can feel how it will be thrown. With a close target that is seen through echolocation, knowing where to throw is merely a bit of practice.

There's a reason ultrasounds are used by animals with biological sonar rather than just passive listening. It offers more reliable images. To see properly using sound, the images have to update constantly.

A loud sound is still loud even if you're not paying attention to it. We imagine that a "sorting system" for sounds would be based in the brain, not in the ears. As such, ears would remain vulnerable to extreme noises or pressure deviances. Mind you, there aren't many people in this RP's world capable of easily generating such noises, so it should not be too high of a risk. 

A brooch or necklace or something like that is something that is much harder to remove. Especially if it is worn beneath clothes/armor. Something hanging from the belt is about as exposed as earrings.