You just gained a level in real life! What class would you take?

[Deophaun]

You are indirectly proving my point. There are ways to fool our ears, but we are so unused to it that it drives us mad!

Not really. It drives you mad with repeated, frequent occurrence. It fools you by making them unpredictable. Yeah, if a sound happens a second time after a short period when you are mentally primed you can zero in on it. But a one off? Not so much. I mean, have you ever had to listen for which battery between three smoke alarms was dying? And that's dealing with something you know about.

Even something as 'subtle' as a Mental display would draw immediate notice and unwanted attention.

No, it wouldn't. Random sounds are a fact of life. Unless you're actively looking for the source, where they come from isn't going to be of much concern to anyone. And even if someone did think that it sounded like it came from inside their head, they're likely to self-diagnose that as a sign of mental instability and try to ignore it, not go running off saying "Quarian is beaming sounds directly into my brain!" No matter how true it is, it sounds insane.

And that could have consequences.

Just not the one's you're thinking.