There are many reasons why your clarinet may be squeaking. Beginners typically find their clarinet squeaks due to an underdeveloped embouchure. This will lessen as you progress and develop better mouth muscles and strong lung capacity for higher registers. When I was a student, I had a habit of biting down too hard on my mouthpiece, contributing to potential squawking. Another beginner habit is putting too much of the mouthpiece in your mouth when you play. Professionals may find that their clarinet is squeaking because it needs new pads, corks, or just needs a general tune-up. Clarinets that are leaking tend to both be breathy when played and squeak consistently.