Factory Sound Dampening

[itln.stln]

I've got a 99 mustang that I'm planning on installing Second Skin throughout, however as I removed the trunk panels and carpet I noticed that the factory had already installed some dampening. My question to you guys is; is it worth the trouble of removing the factory dampening before installing the Second Skin stuff or should it be okay to just lay the Second Skin over the top of it?

Thanks

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[LosIsATool 5,000+ posts]

Lay around it. Doubling a layer is diminishing returns. And if it's like most factory stuff, it's not coming off

 

[itln.stln]

Cool, thanks for the info. While I'm here I might as well ask another question. Is there any benefit to applying sound dampener to the inside of the doors or will it cause issues with the window mechanism?