Its too bad the dealer is too inept to help solve your problem. I had some bad door speaker vibrations in another car after adding an aftermarket stereo system and installed some dynomat sound deadening material to the door behind the speaker. It completely cured the rattle I was getting. You can buy it online much cheaper than at a stereo store, and if you're not comfortable with installing it, any stereo installer could do it for you.
I also have the 20 speaker sound system in the Pacifica, but haven't noticed any vibrations except on a few songs that have a lot of bass when the sound is cranked way up. If I did have vibrations, I would definitely add some dynamat to the panels behind the offending speakers.
2018 Pacifica Limited, w Customer Preferred Package 27P, Trailer Tow Group and Advanced SafetyTec Group
Last edited by Dave S.; 08-08-2019 at 12:06 PM.