Whistling sound
 

Last night I heard a whistling sound coming from my engine. Mostly happens under load, hard to get it to happen by just revving, and it's pretty faint, hard to hear (or maybe disappears) at higher RPMs, once it drops to idle though the sound disappears so I can't pinpoint where it's coming from until I get a buddy to rev it while I listen. In the mean time, what could be the cause of this? Just a blown seal somewhere? I'm hoping this is minor, otherwise the car is going to be sold because this will officially turn it into a money pit.

Someone installed a turbo when you weren't looking??

Look for vacuum leaks first, because that's easy. But normally vacuum leaks are louder at idle because that's when the vacuum is strongest.

Alternators make a whining sound. Can't hear it firsthand so maybe it's really faint & normal. Or it might indicate a diode is failing in the rectifier bridge. You can drive around without the alternator belt installed, because it's not driving the waterpump or anything important.

Haha it actually almost does sound like an itty bitty turbo. I also noticed this morning on my way to work that there is another noise that starts when I'm lifting up on the brake and slowly fades as I put the brake back down. I just go the front brakes done 70 miles ago, hopefully there's not a problem with them already...

It could be an exhaust leak. Check all of your pipes.

Well, how about looking for a vacuum leak somewhere at the vacuum-booster for the brakes.

You might even look around for some soundproofing material across the firewall that has come out-of-place. I had a 2001 Saab that suddenly the turbo was a lot more noticable. Turns out there was a little block of styrofoam glued inbetween the inner & outer fenders directly above the wheel. When it fell out, the normal sound of the turbo suddenly got louder.