Dyanmat is a product used to dampen noise in a car, used by stereo nuts, hot rod guys or people who want to have a quieter car. I've used it with GREAT success in a few normal cars and it works. I used three big packs to cover entire inside (under the carpet and back seat) and inside the doors of a 1979 Honda Accord four door - afterwards it was Mercedes like quiet rather than early "Japanese tin".

Since I've done this on E21, E34 and my current E53 BMW's.

Most car builders put a modest amount (but never enough) on the inner face of the door skin to minimize the drum noise. To prove that it's not enough, go to your X5 and gently tap with your knuckles. You will hear a tin like sound and you do this in various areas around each door. You can eliminate this, which will give you a nicer Mercedes S class sound when you close the door, a quieter car AND the benefit of better audio sound as your system has less road noise interference.

Buy a Dynamat Xtreme bulk pack and the roller. Take your doors apart and apply (you'll cut the part) on the door skin (naturally the side inside the door). You may want to benefit from the operation to upgrade your speakers, change the door vapor barrier foam (by it from your BMW dealer as the parts are custom made for the door), door carriers (before they break) as your doors are "apart".

I did all four of my doors this way (I was upgrading from a cloth to leather interior and changed the door panels as they were part of the package deal). I also put Dynamat on the inside of the rear quarter panels (where the fuses & relays go on the right and some cars have amps and such on the left). Also a bit (not as many places) on the the rear trunk / hatch door (after removing some plastic covers).

Sound of silence is there, and less "drum" reverberation when you close a door or the rear trunk door. For under $200 and your time, make your X5 even quieter ....

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2002 Euro X5 (E53) 3.0 diesel (M57)
5 speed manual with UUC short shifter.
Pre-xDrive NV125 transfer case (chain & gears).
Factory Xenon headlights, Spyder LED tail lights
Updated vortex crankcase breather.
Motorsport dead pedal, factory fire extinguisher, factory first aid kit, factory F&R mud flaps, factory PDC

Bilstein B6 shocks F&R
Redline oil has replaced "lifetime" fluids (F&R diff, manual transmission, transfer case and P/S).
Dimple magnetic drain plugs in all compartments.