Take a look at Trunk Strategies if your vehicle has a trunk and you're still formulating your treatment plan. Rear wheel and exhaust noise are the primary concerns. If your vehicle has a trunk and fold down rear seat backs, you can get a sense of how much noise is entering through the trunk on a test drive with the seat backs down. If you drive an SUV, hatchback or van, the problem is likely worse - your vehicle's rear end in inside the passenger compartment.
Spare Tire Well
The spare tire well, along with the rear wheel arches, are among the most complicated areas because of their compound curves. Very worthwhile to treat. I'm often asked if it isn't just as good to lay the CCF and MLV over the spare well cover. Installation is much easier that way and the performance should be very close although there is always at least a theoretical advantage to placing the barrier as close to the noise source as possible. I always prefer to treat the spare tire well. It keeps the vehicle as close as possible to stock, both in appearance and function and avoids the hassle of a heavy layer between you and the spare well. An hour of extra work is worth the reward.
When it comes to vibration damper, the spare tire well is the most frequently over treated area. This is my first and literally 2nd, 3rd, 4th and 5th efforts to reduce trunk noise. This was in 2005 and the idea was to keep stacking vibration damper until you achieved the result you were looking for. When multiple layers of CLD didn't do the job I added many coats of liquid applied vibration damper. Very little reduction in noise penetration. Worse still, the treatment had effectively knitted multiple panels, each with its own resonant frequency, into a single large structure with a resonant frequency inside the range of the exhaust. I had created exhaust drone in a Honda Civic with a stock exhaust. I tore it all out, replaced it with CLD Tiles™ at 25% coverage and a layer each of CCF and MLV. Made all the difference in the world. There ended up being over 1/2" of stacked vibration dampers when I pulled it out.
The Spare Tire is Part of the Vehicle's NVH System
Sure the spare well is flimsy and resonant - when the spare tire is removed. No where near as much when the spare tire is bolted in place. Notice where the tire makes contact with the well. Stay away from those areas when applying CLD Tiles™, just as you would any other braced or reinforced area.
Take a look at the build logs below. That's really the best way to see how to do it.
We need to find the areas for the horizontal surfaces - the trunk floor and the bottom of the spare tire well, just length * width. Then we need the area of the sides of the spare tire well. If it's a rectangle: (2 * depth * length) + (2 * depth * width). If it's a circle: (2 * 3.14 * radius * depth). Add together for total square inches. Divide by 240 for the maximum number of CLD Tiles™. Divide by 144 for square feet required of each mass loaded vinyl and closed cell foam. Add 3 or 4 Velcro Strips to anchor it all.