My SDL is much quieter than my 300TD for a bunch of reasons, one of the main ones is that there is a sound insulation wall between the engine and the firewall.

They both use the same hood pad, indicating to me that the stock hood pad is sufficient for its purpose.

My thinking is that the source of most of the noise that you hear in the cabin is coming from the firewall, not the hood.

Some other poster created a sound encapusation system for his 300D and posted pics somewhere around here. The main part of that system involved isolating the engine from the firewall with a vertical curtain.

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84 300TD - 235k - Farbe "Surfblau" bought at 213k
87 300SDL - 131k - Farbe "PimpGold" bought at 115k
00 Klepper Faltboot Expedition Double