Here's a description and where I bought them from:

http://www.partsexpress.com/pe/showdetl.cfm?DID=7&PartNumber=299-028

I'm selling a pair of these for $45 and only local pickup please. These things are a little heavy and the shipping alone would be too expensive. ($16 for standard shipping, hence the reason I didn't return them).

I unwrapped them to see where I could fit them in my E, but after I installed my subwoofer I realized I had no need for the extra thump. This would be nice for those using the stock sub but would like the extra vibrations from the low frequencies.

I also believe it will take a little ingenuity and work to install these optimally.