Main floor reinforcement....

Ok, I actually have two problems.
Problem One:
I have a Cape Cod style house with a crawl space. My main floor was getting bouncy. So I decided to run a series of 2"x8" joists under the existing floor the full length of the house. I did this on either side of the center main joist. I also put pylons under the 2"x8" joists to the ground. Now I'm starting to see cracks in my drywall in various places around the house, normally near doorways located along the centerline of the house. Did I screw up by putting in the floor joist reinforcements?
Second, the upstairs floors are horrendously loud and squeaky when walked on. How should I go about quieting those floors? Will running screws down to the joists quiet it down or will I have to remove the first floor ceiling to properly fix this issue.
Thank you in advance for ANY help you could give me.
------------------------------------- SpecialEd <=======}==O
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