I have an '88 260E that I've owned for 10 years now and will probably keep for as long as I can maintain it. I would like to improve the sound insulation aspect of the car. What is possible to add to the stock sound "proofing" that already comes on the car? I've replaced the hood pad but would like to better understand what could be done in the doors, etc. Are there any websites that I should look at?

Thanks in advance.

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Rick in Raleigh
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as of May 2011
'97 S320 LWB 325,000 miles
'88 260E 332,000 miles
'72 220D 338,000 miles (sold)
'73 BMW 3.0si 473,000 miles (retired)