1. No... you don't need a tippet to learn how to cast. The main reason for the tippet is to lengthen your leader or to drop it down one size. For now, don't worry about tippet.
2. The cracking sound you're hearing is probably a result of two things. 1) If you don't have a fly you will often times here this. 2) The major reason is likely because you're starting your forward cast too soon. After your back cast, you must wait until the line gets fairly strait out behind you before you begin your forward cast... otherwise, you're cracking the whip. This is one of the most common mistakes made by new casters. So, pause before you go forward. Also... you can reduce the crack if you will tie a one inch section of yarn to the end of your leader. This will act as the fly.
For the beginner, the fly cast requires you to concentrate on so many things at the same time. There are many different techniques use to teach the fly cast... most are good... some are ****.
Remember these important factors.
1. Don't bend your wrist (bend your elbow)
2. On your backcast, pull the rod up slowly, gradually increasing speed.
3. Power Stroke - At the end of your backcast, you must have a short (few inches) burst of power, flicking it, but don't bend your wrist too much.
4. You must stop your rod at the 12:00 position. Do not go too far back.
5. Wait - Before you begin your forward stroke you must pause for the line to straighten behind you. You can look over your shoulder and watch it for a while if you want.
Eventually, all of this will become second nature to you.
Work on those factors for a while and then report back to us.