Sounds to me like your clutch disc is worn out. When the rivets that hold the friction material to the metal disc start contacting the flywheel it makes a squeaking noise. Thats the sound of your flywheel getting groves in it. Dont take my word for it, get it checked out. If you dont take care of it real soon, you will need a new flywheel in addition to the clutch, pressure plate and throw out bearing.