NVH in automobile

The big hole at rear carrier portion in VW 1302 Super Beetle gave me a good opportunity to think over so deeply about NVH on automobile, the hole had been created after production for the convenience of air-conditioning room equipments.
So the removal of the air-conditioning system means the necessities for several compensations like closing holes at rear compartment.
Also making hole that's unexpected in the original design destroys the balance as a three dimensional body of steel, so to speak the physical property.
Anyway unfavorable conditions must be improved by applying some same kind of material with screws and silicon grue.
The insulating material is needle fuerte insertion between steel floor and the rubber sheet.
This kind of arrangement for preventing NVH would be successful,so I believe.