For me it's a high squeaky "EIIHHH"

And the matching facial expression:
http://15130-presscdn-0-89.pagely.netdna-cdn.com/wp-content/uploads/2014/02/obama-wtf-485x4071.jpg

Mine is "mmhhh?"

Sounds like the first part of this: http://m.youtube.com/watch?v=II2lPcQSzPU

Everything with an exclamation point sounds like when an enemy sees you in metal gear for me

It sounds like Mario jumping
I'm done

I imagine Kaibas face when he loses

Two different sounds for different sources, to me. The first, from a person, is sorta like 'huh' but without opening the mouth. The second, as a displaced sound effect, is the scare chord used when you're spotted in Dishonored.

To me is an expression I can't describe

Mine sounds like "HAHH?!"

Mine makes the stereotypical "EHHH?!" from anime

Mines normally... "the f---?!"

I literally can't describe it its just "?!"

For me, it's the second sound as when you hook a fish on Pokemon.

Mine sounds like "pa-thwoink"

Mine is like eeerrump??

Whaaaaa?!!!???

It makes the cartoon fwee sound

The metal gear sound effect when someone sees you.

Mine is like a crashing window but not as high pitched

It makes a weird, quiet "mmHHHHH?!"

Honestly whenever I see that it makes an old timey car horn sound, like the ones in the movie Atlantis lol

Two consecutive eyebrow raises with a confused face.

In my opinion "?!" is the emoji for "wtf". You have the question mark for "what". Nobody cares about the "the". The exclamation mark is there for "fuck"s sake.

Mine is like that sound solid snake makes once he's spotted but lower pitch

I remember seeing them in comic books like Tintin and the imaginary sound is so strange