I have an 07 TSX - 2.4 Automatic with approx 23K miles. When driving or even at braking. I hear this whistling noise coming from the back. I also notice that there's not much brake pad left in the rear.

Could the noise be coming from the brakes?

It's strange that the rear pads wear out first than the fronts.

Is this normal for all TSX's?

 

I'm at 60K miles and I was at the dealer recently and they gave me some interesting info on my brakes. I got the car at 49K but apparently the rear brake pads had already been replaced but not the fronts. So I guess the previous owner had the same problem you did.

 

hmm.... I recently got my 07 and the back pads are new too at 46k
is that a issue?? but I don't hear any noise.

 

At 23.5k that's very weird but yes the rear pads will make this noise when low. A simple read of the top 10 posts here would reveal other situations just like yours, minus the amount of miles.