Trunk Rattles
 by Eddie Runner (NU5K)

I have posted this info on rec.audio.car several times but the same question keeps getting asked so I thought it should be written where I can find it easier.... 
Here in the tech section is a fine place for it. 

fixing trunk rattles is usually quite a bit different than just sticking dynamat on the inside trunk lid surface.

first you have to identify what exactly is rattling.

the license plate frame is probably one of the most common culprits. Many license plates are only held on by 2 bolts instead of 4 and many license plates have ADVERTISING rings around them that could add to the rattle. You can usually put your finger on it and see if the rattling stops, if it does I put RTV silicone behind it and let it dry, then it wont rattle.

another common problem is air leaks passing through the trunk seal... to isolate this problem I usually lay towels along the trunk seal and close the trunk, if the noise stops then buy a new trunk seal, yours is worn out.

sometimes the trunk lid surface vibrates on the trunk lid cross braces.
run a bead of silicone along the braces and in between the trunk
lid and brace if you can, let it dry and this should stop the 
rattle.

Sometimes it is the car jack, or something in the trunk, wrap it
in a towel and stow it...


Once I had a customer complaining of a rattle, he brought his car in several times and the installers could find nothing wrong. Finally he got SO PISSED AT OUR INCOMPETENCE, that he asked me to go for a ride with him so he could show me the rattle that my installers couldn't find.... 

I found it!

When the customer got into his car he hangs his sunglasses on his 
rearview mirror... The sunglasses rattle like crazy! ha ha ha
Boy was he embarased! ha ha ha

Now, no amount of dynamat is gonna fix your problem if you put the
dynamat where the rattle IS NOT! ... ;-)

First identify where the rattle is, then fix it... 

Dynamat will deaden a panel, it is great for the overall acoustics of the car. I particularly like what it does to a metal door panel when you surround the speaker mounting hole with Dynamat Super. It can make a cheap car seem like your in a QUIET luxurious expensive car.