Turbolag

Hey everyone, this is my first post on the forum.

I have a 2002 mustang gt, and I have two questions I would like to ask.

1. I just noticed this noise coming from the trans, it is like a squeaking noise. But, it makes the noise only when the engine is running and the clutch pedal is fully released. The noise stops when you push the clutch pedal in about 2 inches.
I just installed an adjustable clutch cable also. Not real sure what this noise is.

2. The fuel mileage seems to be way less than I thought. I drove the car about 80 miles the other day and the fuel gauge was almost to full. Once I got back it was almost to half a tank. No idea what's whats wrong.

Here's a little info on the car. I just changed the motor out. It does have some light mods. Headers, cold air intake. It has 3:55 gears

Thanks