What do you mean by "rocking the tower?" What is a tower? Swing sets do make noise but I'm concerned about the "rocking the tower" and the use of the word "terrible." Those two don't sound safe. I wonder if it's installed correctly. I've not seen the wooden sets installed with cement blocks and fence posts. It seems to me that would allow too much movement at the ground level.
If the set is stable, meaning it doesn't actually rock, and the joints are tight, I think it would be safe.
You can also talk with a Rainbow representative. If they have an outlet in your area, go and look at a set. If not call or look them up on the Internet and ask them how best to install it.
Here is an address for their web site that shows pictures and talks about safety. From the picture on this page and on their other pages it appears that the set is designed to sit flat on the ground. I wonder if the noise in yours is caused by the cement blocks and fence posts. I think that the most important part of installation is to be sure the set is level. That means that all parts touching the ground are at the same level. This is a tricky thing to figure out. I think it will take a plumb line and level and I'm not sure how to go about doing the measuring.
You can buy accessories so that the set will sit firmly on un-level ground.
http://www.rainbowplay.com/index.php/rainbow-difference/u...