I used
mineral loaded high density vinyl sheeting to sound insulate a 240D while I still had most of my hearing, with excellent results. This is the stuff used to isulate walls in buildings. It has a thin layer of foam on one side which should be placed against the vibrating surface. I put it along the floor and behind the back seat. It is easy to cut and instal. No glue is needed, the foam will hold it in placeas long as you sandwich it under the carpet. I can not recommend it for use as hood liner material. You can do an entire car for the minimum order amout ($80).

It is heavy but did not seem to effect acceleration. I can still do 0-60 in 30 seconds on a cool day in still air pointing slightly downhill. If there is any interest I will root around and fond/post the supplier info.

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JMF