I didn't read everyone's responses, so someone may have already said it, but the first thing I notice is that you are much to upright with your upper body. Your spine angle should match your calf angle. (/ like the slash, if that makes any sense lol) You look like you are hip thrusting hehe ^^. But it is understandable if you have just gotten back into riding, practice makes perfect! good luck! :)
Edit: I just saw the second video you posted, you seem much more controlled and quieter in this one. That very good :) You are still sitting too far on your tail bone. You should try pivoting your pelvis forward more, (think of like how you stick your but out) that will help with your spine angle as well. The saddle might be too small, but you also make it look smaller by the way you are sitting on it, so trying the above might help that as well. Ask your trainer about it if you are confused :)
Last edited by cosmomomo; 01-18-2011 at 08:11 PM.