So the mod seems to work fine, and it's probably awesome for people who can't hear.

Here's an idea: a hotkey to activate the effect, functioning as a toggle.

You press it, and you see the visual aid.
You press it again, and it stops showing.

Reasons:

From an role-playing standpoint, it would simulate "I'm focusing my hearing" or "I'm paying more attention to the sounds around me."

From another perspective, sometimes it's annoying to have it constantly flashing on the screen, as there's always some noise around that you could simply ignore without much issue, but the aid keeps stealing your attention to it.