Hello, I have a 1985 Nissan PU, 4 cyl, carburated engine. Over the weekend a noise started from the engine area and I don't know what it is. It started rather suddenly and immediately with it came alot more vibration and a small loss of power. The noise is a metal on metal knocking- it is at it's worst when you are just getting going and right after you shift gears. The noise gets faster as you increase the RPM's. Higher RPM's seem to diminish the loudness of the noise as well as the vibration. You can get the noise in neutral but you have to give the engine a real good amount of gas really quick. It does seem to be idling a little rougher but I am not sure. There is alot of vibration. even in neutral when it is idling and no harsh noises are coming from the engine, The cab shakes and so does the stick shift. I took each spark plug wire off, one at a time, trying to see if there was any difference in the noise when I revved it and there wasn't. I also disconnected the alternator belt to see if it was the water pump making noise and that made no difference. As you can see I am stabbing in the dark. Any help at all is highly appreciated.