vibration in rear from subs

[LightningExpo]

hey guys i have a 2001 exped and i have 2 12" subs in the rear behind the 3rd row my question is can anyone help me with fixing the vibration on the back lift gate and i believe the roof as well. i have no idea how to go about this, the vibration just really kills the sound and i want to get it fixed. thanks for your help

 

[BassQuake9000]

Getting dynamat would help. I've got 3 layers of it on my rear door and it helps to keep the bass inside the vehicle, and it reduces the rattling.

 

[LightningExpo]

ive looked into that stuff how do you remove the plastic on the rear door? and how much did you spend for 3 layers? thanks for your help