Speaker Rattling

[kylemhall]

Hello All,
I thought I would replace my factory speakers in hopes of getting better sound out of my system. I purchased a set of Rockford Fosgate Prime 6.5" speakers ( http://www.amazon.com/gp/product/B00...ef=oss_product ). I have replaced one speaker so far, the rear right hand speaker.

What I have found is that the new speaker seems to have less bass than the factory speaker in the rear. Furthermore, it seems to be vibrating the car body. I used 1/4" MDF to make my spacer. I'm pretty sure I installed it tight and solid, so it's not the speaker rattling against the body, it seems that the speaker and body are vibrating together. Could this explain the loss of bass compared to the OEM speaker?

I've been looking at all the previous posts about speaker replacement. It looks like dynamat may fix this problem, but I would love to avoid anything that invasive unless I have to.

Any advice on what I can do would very appreciated.