Welcome to the forum, glad you found us. It's hard to diagnosis without actually seeing your cast-- but there are a couple common problems you may be running into...
-Not waiting for the line to straighten out completely on the back cast. What happens is you may be starting the forward cast while there is still some slack in the backcast because it hasn't fully straightened out. The rod is moving forward with out being under any load (bend) until it takes up the slack. When it takes up the slack and is moving forward the tip suddenly loads and recoils by unloading sending shock waves down the line- all as you're moving the stroke forward. Since the path of the line always follows the rod tip, this sends waves down the fly line.
-Starting the forward cast too fast and slowing down on the forward stroke. Again if you start too fast and slow down on the forward cast, the rod tip takes a sudden bend at the start of the cast, and your stroke can't keep up with the rod's natural tendency to unload. The rod will recoil by unloading (straightening) sending shock waves into the line. The could be a good possibility if you are throwing a "tailing loop" and getting overhand knots in your leader or tippet (called "wind knots")
Some things to try-
open up your stance a bit to be able to watch your back cast-- wait for it to straighten (if you hear "crack the whip sounds" you're not waiting long enough for the line to straighten)
Try "drifting back" with your rod hand before beginning the forward cast. Not by lowering the tip-- but by just sliding your arm back a bit--- this will counteract the tendency many people have (including me) to start too soon and too fast on the forward stroke. See if that helps a bit and let us know.
On the forward stroke, ideally you want a smooth acceleration and then sudden stop, rather than a fast start, slowing to a tentative stop. You also want the rod tip to be moving in the same plane horizontally to get a tight loop, rather than an oval path which will cause a wide loop---- the path of the line follows the tip of the rod.
The best way I've heard the forward cast explained is to imagine you have a big poisonous spider on the top of your rod, and a 10' wall a few feet in front of you. You want to start the forward stroke slowly, accelerate, then stop suddenly to flick the spider over the wall. If you start the forward cast too fast, the spider will drop on your head
Watching some one like Joan Wulff cast is very instructive. Now in her 80's, and all of 90lbs soaking wet, she manages to throw a beautiful line-- using timing and smooth acceleration and sudden stops rather than brute power and strength.
One thing that will probably help enormously is to get some casting lessons- local shops often have classes, offer inexpensive lessons or they may just take you out back for a quick tuneup. There are also groups like the Federation of Fly Fishers that have affiliated clubs all over the country. They have casting clinics, informative meetings, group trips, and are very welcoming to new members. You can do a search here to see if there's a FFF affiliated club near you: http://www.fedflyfishers.org/Default.aspx?tabid=4357
You can also go to the "instruction" link on FFF site to do a search for certified fly casting instructors. The advantage of getting an instructor early in the game is that as you practice you'll be practicing good technique rather than "hard wiring" poor techniques into your practice--- and it's a good idea to get periodic tune ups.
Good luck, and keep asking questions. And let us know where you are-- we have members all over the place on this forum and they may be able to suggest some great local resources near you.