Doesnt happen everytime I drive but every once in a while, especially on more humid days, when I press the brakes gently I hear a harsh squeak, almost like a loud whistling from the brakes and I have no idea what it is.

113,000 '07 tl-s

 

I get it sometimes when I back up.
I'm still wondering what causes my squeeking

 

When stopping apply more pressure to the pedal, noise stops? If so, on light application the pads move ever so slightly inside the caliper and therefore the metal to metal noise, but under hard pressure they stay put, so pull the pads and apply some anti-squeal paste.

Example:
http://compare.ebay.com/like/1108761...Types&var=sbar

 

What kind of pads are you using?

 

I havent changed the pads since I bought the car and i have no idea if the previous owner did so im guess still manufacture pads

 

The Brembos on the Type-S/6MT are prone to squeaking under light brake application. Happens to me when I'm pulling into parking spaces sometimes.

Regreasing the pads and pins at their contact points should do the trick.