I need to deaden my trunk. The rattling from the trunk lid sound terrible outside the car. I can't decide between going with either the Second Skin Damplifier or the Spectrum brush on. Anyone got any recommendations?
Here is what I did with my trunk lid. I took 2 cans of that expanding foam stuff and sprayed it in between any 2 adjoining pieces of sheet metal (like 2 large flate pieces) any in between any metal bracing and the lid itself. I took deader and covered around 50% of the whole lid and I was done. The trunk lid now feels 5x heavier than before. I have to lower it down most of the way slowly then drop it to shut it. Some people take the hook that the lid latches to when closed, and lower it so it will be tighter. There's no way that it will rattle if you do this. Also make sure you use the tiles inside the trunk. Closed cell foam behind the license plate, and if you are still experiencing rattles, look to your bumper. A lot of times, and I know on my car, people have plastic bumpers that attach to sheetmetal. This too can resonate, but I would look to fix your trunk first and license plate to see how this works out for you.
I'd try and figure out exactly what is rattling. It might just take a squirt of foam in the right place to make it quiet. Playing continuous sine wave tones from a variable frequency source is a good way to locate specific rattles and buzzes. As you sweep the frequency, different parts will resonate and you can fix them one at a time.
It's possible that some things will only respond to loud thumps... since playing really loud bass continuously will be tough on amps and speakers (and neighbours), maybe you could run a drum synth program and use thumps at various frequencies. Or a software tone burst generator.