Can someone educate me on what exactly this is? I am hearing a hissing sound new my power steering/engine area. This only happens when I hit around 2½ RPMs. Someone told me it may be my brake booster. Also starting to hear a squishy sound coming from the brakes.

to put it simply, the brake booster takes vacuum created by your engine, and uses it to make it easier to push the brake pedal.

Thats putting it VERY simply, but gives you an idea.

Being that you are hearing a hiss, you most likely have some type of vacuum leak, if it is that audible, I would try to track it down by ear.....if it happens to be the brake booster, than so be it, but it could very easily be a hose either broken or disconnected.