Every time I hit the speed bumps on my block I can hear a rattle from the front end. What can this be?

 

Without more info I'd start by checking the front control arm bushings and motor mount.

 

Front control arm bushing seem hard to change. Is this true? Is it worth going with alta? Whats easier to install?

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off topic nice website....
Those Megan coil overs look like they have the strut tower reinforcement plates. Is that correct? How do you like them compared to KW?

 

Maybe it is just a heat sheild or your exhaust hitting something. I would jack up the car, support with jack stand, crawl under the car, and pound/wiggle various items to see if you can reproduce the noise.