Please explain why Diesel engines (in general):
I understand in principal how both engine types work so feel free to go into technical details. My assumption is that it probably has to do with the higher compression ratio of the Diesel engine.
You are absolutely right that the high compression ratio is the cause - you end up with a much greater pressure variation in the combustion chamber. See this question for explanation about the noise.
And the vibration is also directly related to this. With a bigger pressure differential, everything moves and vibrates more.
