Targeting the rattle is the key. Spoilers will allmost always rattle, fact of life.

 

Sheet metal flexing means that the metal is too thin. Add more weight to it. Sound deadener should fix it.


How is the spoiler rattling? Is it mounted loose? Is spoiler flexing? Turn up the music and push the spoiler down onto the trunk putting your weight over its mounting points. If that stops it, you need to secure it more tightly. Then try putting weight on the spoiler to see if its flexing and making noise. You can do this by maybe clamping your hands and squeezing the middle of it.