Motor dies after startup.

The clatter sound is not high pitched but kinda low. I hear it only at idle (it's the loudest in reverse) and when I try to accelerate it increases in intensity but when I take the foot off the pedal it immediately goes away.

After I finish this oil change and putting in new coolant I'm going to check for vacuum leaks and then I'm going to pull the plugs. (I have a guide to reading the plugs somewhere, if not, I can google it.)

As far as someone else's suggestion to drop the tank, I see where you're coming from. And it's likely my fuel tank is gunked up, but at the moment it's not an option.

I also wonder if maybe some of the plugs are not firing. I'm also going to check my distributor wire to coil and wires to sparkplugs.