Engine noise?
 

I have a 78 300d and i was wondering what the sound i am hearing might be. When the car is running and in park it sounds kinda loud, until i push on the gas, ever so slightly, then it doesnt sound as loud. When i was reading some of the older posts i seen something about compression and taking the oil cap off. When i take the oil cap off with the car running i see a very little bit of smoke and no oil comes splashing out. When i asked someone i knew what it might be, they said that i might be losing compression somewhere. So now i am puzzled!? What might the loudness of the engine and the steam mean, and what might need to be done?