Making sounds louder is dangerous if you don't have really strong filters. A sudden, unexpected boom while that "boosting" is active has a decent likelihood of damaging hearing. If you're reliant upon others making sound, then eventually there will be some sneaky bastard you can't "see" because he or she doesn't make enough noise. Someone who can breathe silently enough not to be heard even by a master listener. And if he or she is heard, he or she can simply make a massively loud noise, causing incapacitation, and still have the advantage. 

We like the idea of playing with a sound-based power, but we think you could go with solutions for it that leave your character less prone to incapacitation. 
One possible way of doing it is to have your relic grant your character the ability to both perceive and generate ultrasound, much like the bio sonar of numerous animals. That way, you won't have him as vulnerable to loud noises, and you're not reliant upon others making the noises you need to "see". 

As for the vulnerable placement of the earrings:
Just because you can hear something coming, does not mean you can always dodge it. Thats why armor, when it was invented, covers areas the user can see as well as those he/she cannot see. Where others would look strange with one (or both) ear(s) cut off, your character would be dead if that happened.
Its a bit like the myth of Achilles. Why, if his weak point was the achilles heel, was that part not given extra armoring? We're not saying you should absolutely not use earrings (it is after all, as Sparks so aptly put it, a personal preference), but it will be a significant risk for him if you do. We're sure there's some pretty bauble you could go with that is not as likely to be cut off by chance in combat or dropped by accident. We're not going to suggest anything specific here, as it should be your choice what you go with.

The idea above should leave your character more powerful than before, we're not the sort to suggest stuff to weaken PCs without good reason (i.e. if they're ridiculously Overpowered). Its more fun when they're strong.