Quieting a 300 Tdi - QuietCar coatings
I wrote earlier that i was going to try QuietCar on the bonnet underside to quiet the 300 Td.i After much hesitation (it was newly painted and pristine) I finally did. It goes on very easily, with minimal overspray and takes about 7 days to cure. I used 1/2 gallon ($58 per gallon) and it added about 5 pounds to the bonnet weight. The bonnet definitely feels more substantial now and I think it did help quiet the underhood noises but the biggest improvements came from the thick rubber firewall pads and floor mats that RN sells. Only drawback is that they need some help staying up in hot weather. They simply buckle and fall on your toes unless you anchor them some way. Also a Magnaflow flow-through muffler took the sharpest rap out of the exhaust and with no loss of power.
I think the QuietCar helps and would be excellent sprayed on the inside of the doors where you would put DynaMat. It is black and looks a lot like Line-X or Rhino coatings. I've used Dynamat on the doors before which helped the output from the door speakers substantially and the doors then close with a satisfying "thunk".
If I could find a good sound absorbent material to glue to the Quietcar I think I would be doing about all I could to quiet the D90. Any ideas?