The replacement rear ends out there for HI-PO applications have some pretty noisy gears. The 9" is the worst, the 8.8 comes in second and may even be on par with some rather noisy stockers we've seen.

The rear end of our trucks have extremely limited sound deadening capabilities, so I'm planning to mitigate the gear whine problem with soundproofing. I hope not to add too much weight back there, maybe 25lbs at the most, but I'm going to start with a layer of Dynamat Xtreme from the rear seats, all the way to the tailgate. Then come on top of it with 1/4-1/2" of sound foam, then slap on the stock carpet and sound material.

Hopefully this layered approach will seriously cut down on the Decibles in the cabin.

Anyone have any idea how much Dynamat our trucks would need? The bulk packs come in 36 sq ft cartons... sounds like plenty for a car.

well my back end is Dynomatted a bit for the stereo setup i got (and still got rattles. lol). pretty sure it quiets it down a bit as far as "outside cabin" noise, but got to wonder how much added weight in dynomat i got on the rig.
think they used 1.5 to 2 rolls on my install.

I had my mustang dynomatted. Its pretty heavy stuff. From my experience with it you would need a good amount to have a decent affect on your exterior noise problems. Which would add a good amount of weight.

One box should cover you for the rear. Mine is covered, and it helps a good bit. Just take off the rear trim and remove the cargo tray base and peel away. I've also covered the rear seat and foot well area and passenger side floor. Just haven't gotten to the driver's side yet. you might want to try to get up the sides of the rear compartment if you can, and the liftgate behind the plastic. Every little bit helps. Cumulatively, not my et's but the dd comfort is worth the miminal sacrifice.

Is this stuff really heavy??

Hmmm....this is a good idea...wondering how heavy it actually is though...keep us updated Winston!

Winston your math is pretty good. Figure out how much weight you'll be adding. This is how much it weighs per cubic foot.

Mass:
0.45lb./ft2 (2.20kg/m2)

I've found for pure sound absorption Hushmat Megabond is my favorite.

http://www.hushmat.com/HR_Megabond.php They reccomend using it over the Hushmat Ultra, but I think for your application the Megabond by itself is enough. The floor seems to be insulated enough from temperature, as it does not get too warm back there, and it does not have a "Tinny" sound, so I don't think you need the added weight of the ultra under the megabond. This stuff is foam based and much lighter than the tar or rubber based Ultra mat or Dynamat.

I have a pretty good hookup for pricing on this stuff, PM me if you are interested.

i wouldnt do it as personally i feel it reduces sound very little depending on how much you put, meaning you need a lottttt to have nice noticeable effect and it will add a lotttt of weight for sound improvement. Its really just useful for high-audio application imo, unless you relly hate the sound of the performance rears, personally never heard how loud they are but id imagine not louder than some subs pounding in back hahah, GL with it all who go that route ;)

Let us know Winston.
Bill

I was going to sound proof a room I had but moved before I double densitied the walls. I came across something called Green Glue. It turns sound energy into heat and is something the pros use to sound proof stuff. They put it between the soundproofing barriers. It creates air pockets that the sound travels in and around and then when the sound hits the GG, it goes from sound to heat energy. I was thinking of dynomatting my rear with the GG. Perhaps this spring. I have an entire case of the stuff. If I do it, I'll document it and see how it goes. The important thing to remember is that density works with layers and with air pockets in between overall works well. Having gaps in locations is where the sound will get through.

I took out the cargo tray and removed the rear plastic panels up to the back seats. Then I sprayed bed liner material I got at the auto store on the floor and up the sides to the windows. This worked to deaden the tinny sound. Make sure you can let it air out for a day before you have to drive to far.

Get a louder exhaust or a louder stereo !!!

I understand the title of the thread, however I have done this to my previous vehicle.... the Lightning. Overall it was really simple, not much inside of the L so covering it was an easy saturday job. I guess I'm comparing apples to oranges tho, because the L was noisy inside from the get go really, and the Jeep seems so quiet to me (other than the tires). After the dynamat, it did get pretty quiet, but then there were the squeaks from other things inside the cabin that I started to notice lol. I was never concerned about the weight, and adding an extra 25-30 pounds would never be noticed, unless measured in hundreths, if not thousands, of a second.

Ebay is where I got it originally. Not sure if you have your own vendor or not, but Ebay has decent prices on the stuff:
http://cgi.ebay.com/Dynamat-Extreme-10455-Bulk-Pak-36-SQ-Feet-Brand-New_W0QQitemZ320345596371QQcmdZViewItemQQptZLH_Def aultDomain_0?hash=item320345596371&_trksid=p3286.c0.m14&_trkparms=72%3A1234%7C66%3A2%7C65%3A12%7C39%3A1%7C 240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50

Im sure sometime in the future I will do it to the Jeep as well, as I did like the outcome from the L. But right now Im content :)

Anyways, just my .02.